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  • 1
    Digitale Medien
    Digitale Medien
    The Maillard reaction in vivo (1991)
    Springer
    European journal of nutrition 30 (1991), S. 29-45 
    Details
    ISSN: 1436-6215
    Schlagwort(e): advanced glycosylation endproducts (AGE) ; ag(e)ing ; aminoguanidine ; ascorbate ; autoxidation ; biomarker ; browning reaction ; chemical modification of proteins ; diabetes ; glycation ; glycoxidation ; nonenzymatic glycosylation ; oxidation ; Maillard reaction ; Aminoguanidin ; Ascorbat ; Autooxidation ; Biomarker ; Bräunungsreaktion ; chemische Veränderung vonProteinen ; Diabetes ; Glycosylierung ; Glycoxidation ; nichtenzymatische ; Glycosylierung ; Oxidation ; Maillardreaktion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft , Medizin
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Die Maillard- oder Bräunungsreaktion genannten Umsetzungen zwischen reduzierenden Zuckern und Eiweiß führen zur chemischen Zerstörung der Aminosäuren und zum Verlust der Proteinqualität während der Lebensmittelbearbeitung und -lagerung. Der vorliegende Beitrag zeigt Befunde auf, daß die Maillardreaktion auch im Gewebe des Menschen bei der Alterung von Proteinen mit langer biologischer Halbwertszeit auftritt. Die Konzentrationen an den sogenannten Amadori-Produkten, die im Initialstadium der Maillardreaktion aus Glucose und den Proteinen der Augenlinse oder dem Kollagen der Haut entstehen, erwiesen sich als relativ konstant, auch mit zunehmendem Alter. Die Produkte der Glycosylierung und nachfolgenden Oxidation der Proteine, auch Glycoxidationsprodukte genannt, häufen sich dagegen im Alter an, und zwar bei Diabetikern in vermehrtem Maße. Zu diesen Produkten gehören die Aminosäurenderivate N-(carboxymethyl)-lysin (CML), N-(carboxymethyl)-hydroxylysin (CMhL) sowie das fluoreszierende Quervernetzungsprodukt Pentosidin. Während diese Glycoxidationsprodukte in den Körpergeweben nur in Spuren vorkommen, gibt es deutliche Hinweise auf die Anwesenheit weiterer Bräunungsprodukte, deren Charakterisierung jedoch noch aussteht. Es werden Möglichkeiten zur „Entgiftung“ der reaktiven Zwischenprodukte aus der Maillardreaktion sowie zum Abbau extrem gebräunter Proteine diskutiert sowie neuere Möglichkeiten zur therapeutischen Modulierung fortgeschrittener Stadien der Maillardreaktion aufgezeigt.
    Notizen: Summary The Maillard or browning reaction between reducing sugars and protein contributes to the chemical deterioration and loss of nutritional value of proteins during food processing and storage. This article presents and discusses evidence that the Maillard reaction is also involved in the chemical aging of long-lived proteins in human tissues. While the concentration of the Amadori adduct of glucose to lens protein and skin collagen is relatively constant with age, products of sequential glycation and oxidation of protein, termed glycoxidation products, accumulate in these long-lived proteins with advancing age and at an accelerated rate in diabetes. Among these products are the chemically modified amino acids, Nɛ-(carboxymethyl)lysine (CML), Nɛ-(carboxymethyl)hydroxylysine (CMhL), and the fluorescent crosslink, pentosidine. While these glycoxidation products are present at only trace levels in tissue proteins, there is strong evidence for the presence of other browning products which remain to be characterized. Mechanisms for detoxifying reactive intermediates in the Maillard reaction and catabolism of extensively browned proteins are also discussed, along with recent approaches for therapeutic modulation of advanced stages of the Maillard reaction.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01910730
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  • 2
    Digitale Medien
    Digitale Medien
    Ni–Zn–P alloy deposition from sulfate bath: inhibitory effect of zinc (1999)
    Springer
    Journal of applied electrochemistry 29 (1999), S. 1171-1176 
    Details
    ISSN: 1572-8838
    Schlagwort(e): alloys ; cyclic voltammetry ; electrodeposition ; electroless deposition ; nickel ; phosphorus ; zinc
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract Electroless Ni–Zn–P alloy deposition from a sulphate bath, containing sodium hypophosphite as reducer, was investigated. To increase the plating rate, the deposition parameters were optimized. The effect of process parameters (T, pH and [Zn2+]) on the plating rate and deposit composition was examined and it was found that the presence of zinc in the bath has an inhibitory effect on the alloy deposition. As a consequence, the percentage of zinc in the electroless Ni–Zn–P alloys never reaches high values. Using cyclic voltammetry the electrodeposition mechanism of Ni–Zn–P alloys was investigated. It was observed that the zinc deposition inhibits the nickel discharge and, as a consequence, its catalytic activity on hypophosphite oxidation. It was also found that increase in temperature or pH leads to the deposition of nickel rich alloys.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1003426904395
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  • 3
    Digitale Medien
    Digitale Medien
    Structure of (meso-5,10,15,20-tetraphenylporphyrinato) dichlorophosphorus(V) chloride, [P(tpp)Cl2]+Cl− (1995)
    Springer
    Journal of chemical crystallography 25 (1995), S. 231-235 
    Details
    ISSN: 1572-8854
    Schlagwort(e): Octahedral ; phosphorus ; chloride
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Physik
    Notizen: Abstract The title compound [P(tpp)Cl2]+Cl− crystallizes in the space group P21/n witha=10.701(2),b=24.860(2),c=14.799(2), β=94.24(2)°,Z=4. The phosphorus atom has an octahedral coordination geometry formed by the four nitrogen atoms (Np) of the porphyrinato group and the two chloride ions. The average phosphorus-chloride distance is 2.150(1) Å, with phosphorus situated 0.006 Å below the porphyrin ring.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01665175
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  • 4
    Digitale Medien
    Digitale Medien
    Oxidation of bridging groups by carboxylate coordinated ligands in palladium clusters (1992)
    Springer
    Journal of cluster science 3 (1992), S. 411-421 
    Details
    ISSN: 1572-8862
    Schlagwort(e): Palladium ; carbene ; oxidation ; phosphonate ; carboxylate
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Thermolysis of tetranuclear palladium clusters Pd4(μ-Q)4 Pd4(μ-Q)4(μ-O2CR)4 (Q=CPh2 or CO;R=Me, CMe3, Ph, CH2Cl or CF3) has been found to involve innersphere oxidation of carbene or carbonyl ligands during which an oxygen atom transfer occurs from the carboxylate group to the carbene or carbonyl ligand. The thermolysis of the carbonyl clusters gives rise to the products of CO2 insertion into the C–H bond of benzene or toluene used as solvents forming benzoic acid from benzene and a mixture of phenylacetic and toluic acids from toluene. The reaction of [Pd(OAc)2(PPh3)]2 with HCO2H includes the transfer of an O atom from formate ligand to the P atom and cleavage of the P-Ph bond accompanied by transfer of the Ph group from PPh3 ligand to the palladium atom. The structure of the complex formed, [Pd(μ-O2PPh2)(C6H5)(PPh3)]2, has been resolved by X-ray analysis.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00702748
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  • 5
    Digitale Medien
    Digitale Medien
    Chemiluminescence in evaluating the thermal oxidative stability of acrylonitrile-butadiene-styrene (ABS) copolymers. II. ABS/polycarbonate (PC) blends (1993)
    Springer
    Journal of polymers and the environment 1 (1993), S. 275-279 
    Details
    ISSN: 1572-8900
    Schlagwort(e): Chemiluminescence ; oxidation ; stability ; acrylonitrile-butadiene-styrene (ABS) ; ABS/polycarbonate blend
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Energietechnik , Maschinenbau
    Notizen: Abstract The thermal oxidative stability of various ABS/PC compounds was studied by means of the chemiluminescence technique. Similarly to pure ABS, Irganox 1076 and Irganox MD 1024 perform as moderate antioxidants in ABS/PC and (ABS/PC + lubricant) blends. Neither Tinuvin 144, Irgaphos 168, nor their mixture affects the durability of the ABS/PC blend. At the same time, (Irgaphos 168 + Tinuvin 144) in combination with Irganoxes was found to provide a noticeable enhancement in durability to the (ABS/PC + lubricant) system. Titanium dioxide pigments by themselves have only a slight influence on the oxidative stability of the ABS/PC blend. Durability of the (ABS/PC + pigment) and (ABS/PC + lubricant) systems was found to be the same and the overall protective effect of Irganox 1076 was similar in both the (ABS/PC + lubricant) and the (ABS/PC + lubricant + pigment) systems. Certain modifiers significantly improve the durability of the ABS/PC compounds, although their function may differ in the systems with and without pigments.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01458294
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  • 6
    Digitale Medien
    Digitale Medien
    Chemiluminescence in evaluating the thermal oxidative stability of acrylonitrile-butadiene-styrene (ABS) copolymers. 1. Influence of stabilizers and lubricants (1993)
    Springer
    Journal of polymers and the environment 1 (1993), S. 107-110 
    Details
    ISSN: 1572-8900
    Schlagwort(e): Chemiluminescence ; oxidation ; stability ; acrylonitrile-butadiene-styrene (ABS)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Energietechnik , Maschinenbau
    Notizen: Abstract The influence of lubricants, UV stabilizers, antioxidants, and metal deactivators on the resistance of ABS to thermal oxidation was studied by means of the chemiluminescence technique. Neither of the additives seems to affect significantly the induction period of oxidation. At the same time, the influence of various additives on the oxidation rate constant is remarkably different: the introduction of lubricants and UV stabilizers increases its value, while antioxidants and metal deactivators have the opposite effect. For the particular systems studied durability is decreased in samples containing the lubricant and UV stabilizers and increased in samples stabilized with the antioxidant and metal deactivator.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01418203
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  • 7
    Digitale Medien
    Digitale Medien
    Electrochemical characterization of Fe-Ni-P alloy electrodeposition (1997)
    Springer
    Journal of applied electrochemistry 27 (1997), S. 1198-1206 
    Details
    ISSN: 1572-8838
    Schlagwort(e): alloy ; amorphous ; anomalous ; hydrogen ; iron ; nickel ; phosphorus ; plating
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract In this study we have investigated the electrodeposition of amorphous iron–nickel–phosphorus alloys from a sulfate electrolyte. Fe-Ni alloys are known to exhibit an ’anomalous‘ type of plating behaviour in which deposition of the less noble metal is favoured. We have found that the codeposition of phosphorus from hypophosphite in the electrolyte led to a reversal to a ’normal‘ behaviour. This reversal was due both to the suppression of iron and enhancement of nickel partial currents. The overall deposition process is dominated by the hydrogen evolution reaction. This is exacerbated by the low pH needed to codeposit sufficient phosphorus to achieve an amorphous structure.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1018475718629
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  • 8
    Digitale Medien
    Digitale Medien
    Carbon monoxide electrooxidation on porous Pt–Ru electrodes in sulphuric acid (1997)
    Springer
    Journal of applied electrochemistry 27 (1997), S. 1275-1282 
    Details
    ISSN: 1572-8838
    Schlagwort(e): Carbon monoxide ; Pt-Ru/C catalyst ; Tafel slopes ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract CO electrooxidation on a Pt–Ru/C catalyst was investigated in sulphuric acid electrolyte. The physico-chemical properties of the Pt–Ru/C catalyst were studied by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The influence of temperature, CO partial pressure and proton concentration on the electrochemical oxidation rate was investigated by steady-state galvanostatic polarization measurements. The apparent activation energy decreased from 70 to 30kJmol−1 as the overpotential increased from 0.5 to 0.9V vs NHE. The reaction order with respect to carbon monoxide increased, passing from 0.4 to 1, with the increase of the overpotential from 0.5 to 0.7V vs NHE; a reaction order close to −1 with respect to the protonic concentration was observed, irrespective of the potential. Tafel slopes of about 136mVdec−1 were determined for oxidation of CO and CO/N2 mixtures.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1018492122263
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  • 9
    Digitale Medien
    Digitale Medien
    Characterization and stability of doped SnO2 anodes (1998)
    Springer
    Journal of applied electrochemistry 28 (1998), S. 607-612 
    Details
    ISSN: 1572-8838
    Schlagwort(e): SnO2 anodes ; doping ; high overvoltage anodes ; surface analysis ; oxidation ; water treatment
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract Doped tin dioxide electrodes have been prepared by a standard spray pyrolysis technique. The electrochemical behaviour of these electrodes has been investigated by cyclic voltammetry in sulphuric acid using the Fe2+/Fe3+ redox couple system as test reaction. Oxygen evolution has been used to study the stability of doped SnO2 electrodes. The SnO2 electrodes doped with antimony and platinum exhibit the highest stability. XPS analysis shows that the oxidation state of Sn, Sb and Pt are +4, +3 and +2, respectively, the probable species being SnO2, Sb2O3 and PtO.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1003250118996
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  • 10
    Digitale Medien
    Digitale Medien
    Microstructural characterization and corrosion resistance of Ni–Zn–P alloys electrolessly deposited from a sulphate bath (1999)
    Springer
    Journal of applied electrochemistry 29 (1999), S. 637-645 
    Details
    ISSN: 1572-8838
    Schlagwort(e): alloys ; electroless ; microstructure ; morphology ; nickel ; phosphorus ; zinc
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract Electroless Ni–Zn–P alloy coatings were obtained on an iron substrate from a sulfate bath at various pH values. The effects of changes in bath pH on alloy composition, morphology, microstructure and corrosion resistance were studied. Scanning electron microscopy was performed to observe the morphological change of the deposits with bath pH. Coating crystallinity was investigated by grazing incidence asymmetric Bragg X-ray diffraction and transmission electron microscopy. A transition from an amorphous to polycrystalline structure was observed on increasing the bath alkalinity, and thus decreasing the phosphorus content of the alloys. A single crystalline phase corresponding to face-centred-cubic nickel was identified in the alloys obtained from a strong alkaline solution. An increase in zinc percentage up to 23% in the deposits does not change the f.c.c. nickel crystalline structure. Corrosion potential and polarization resistance measurements indicated that the corrosion resistance of electroless Ni–Zn–P alloys depends strongly on the microstructure and chemical composition. The deposits obtained at pH 9.0–9.5 and with 11.4–12.5% zinc and 11.8–11.2% phosphorous exhibited the best corrosion resistance.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1026441403282
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  • 11
    Digitale Medien
    Digitale Medien
    Phosphazene-bound Rose Bengal: A novel photosensitizer for singlet oxygen generation (1991)
    Springer
    Journal of inorganic and organometallic polymers and materials 1 (1991), S. 389-395 
    Details
    ISSN: 1572-8870
    Schlagwort(e): Poly(organophosphazenes) ; cyclophosphazenes ; Rose Bengal ; photosensitization ; singlet oxygen ; oxidation ; heterogeneous phase photosensitizer ; 1,3-diphenyl-isobenzofuran
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract In this paper we report the synthesis and the characterization of cyclo- and polyphosphazenes supporting Rose Bengal. These substrates are suitable for the photosensitized generation of singlet oxygen, both in homogeneous and in heterogeneous phase. The efficiency of1O2 production has been measured in homogeneous solution using, as photosensitizer, the cyclophosphazene-bound Rose Bengal and considering, as testing reaction, the oxidation of 1,3-diphenylisobenzofuran; it was found comparable to that of free Rose Bengal in the same experimental conditions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00702501
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  • 12
    Digitale Medien
    Digitale Medien
    Biomass conversion: attempted electrooxidation of lignin for vanillin production (2000)
    Springer
    Journal of applied electrochemistry 30 (2000), S. 727-731 
    Details
    ISSN: 1572-8838
    Schlagwort(e): electrosynthesis ; oxidation ; lignin ; vanillin
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Abstract Electrochemical oxidative degradation of Kraft lignin was investigated in batch and flow cells on Pt, Au, Ni, Cu, DSA–O2 and PbO2 anodes. Production of vanillin was evaluated by means of formal kinetic analyses. Conversion and chemical yields were found to be dependent mainly on the applied current density, that is on the partial pressure of oxygen at the interface, while the nature of the electrode influenced the reaction rates.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1004003613883
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  • 13
    Digitale Medien
    Digitale Medien
    Synthesis and crystal structure of 1-acetyl-3-bromo-3-phenylazetidine and 1-phenyl-2-(N-acetyl-N-formyl)-aminoethanone (1998)
    Springer
    Journal of chemical crystallography 28 (1998), S. 119-123 
    Details
    ISSN: 1572-8854
    Schlagwort(e): Azetidine ; azetine ; ring opening ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Physik
    Notizen: Abstract 1-Acetyl-3-bromo-3-phenylazetidine (1), C11H12BrNO, has been synthesized and characterized by spectroscopic methods and single crystal X-ray analysis. It crystallizes in the space group P2 1/c with a = 8.633(1), b = 7.461(1), c = 17.204(1) Å, β = 98.403(7)°, V = 1096.2(2) Å3, Z = 4, D calc = 1.540 g cm−3. The azetidine ring is nearly planar since the four atoms are within ±0.039(5) Å of the mean square plane calculated for the heterocycle. The attempt to obtain a highly strained 2-azetine derivative from the above compound gave, surprisingly, 1-phenyl-2-(N-acetyl-N-formyl)-aminoethanone (2), C11H11NO3. This compound has been also characterized by spectroscopic methods and single crystal X-ray analysis. It crystallizes in the space group P212121, with a = 5.4719(3), b = 8.3205(6), c = 23.298(3) Å, V = 1060.7(2) Å3, Z = 4, D calc = 1.286 g cm−3. The aminoethanone residue is in a near planar conformation where the torsion angles are 7(2)° for N–C–C–=O and −173(2)° for N–C–C–C(Ph).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1022489729966
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  • 14
    Digitale Medien
    Digitale Medien
    Oxidation of 3-methylindole catalyzed by cobalt(II)phthalocyanines covalently bound to polyorganosiloxane (1991)
    Springer
    Journal of inorganic and organometallic polymers and materials 1 (1991), S. 211-221 
    Details
    ISSN: 1572-8870
    Schlagwort(e): Polyorganosiloxane ; cobalt(II)phthalocyanine ; polymeric catalyst ; oxidation ; 3-methylindole ; polymer conformation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Two kinds of cobalt(II)phthalocyanines covalently bound to polyorganosiloxane (POS) were prepared to be applied as catalysts for the oxidation of 3-methylindole in organic solvents. The catalytic activity of the POS whose carboxyl residues were methyl-esterified was high compared with that of the POS which has carboxyl residues. The former polymeric atalyst exhibited higher catalytic activity than monomolecular phthalocyanine, indicating an appearance of effects of polymer chains. The factors which influence the catalytic oxidation, e.g., polymer conformations, basicity of solvents, and equilibrium involving phthalocyanine monomer and the dimer, are discussed. It has become apparent that polymer conformation influences catalytic activity and that the catalytic activity of the POS, whose main chains are mobile, is high.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00701320
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  • 15
    Digitale Medien
    Digitale Medien
    Chemiluminescence in evaluating thermal oxidative stability of acrylonitrile-butadiene-styrene (ABS) copolymers. III. Emulsion-grade products (1995)
    Springer
    Journal of polymers and the environment 3 (1995), S. 199-203 
    Details
    ISSN: 1572-8900
    Schlagwort(e): Chemiluminescence ; oxidation ; stability ; acrylonitrile-butadiene-styrene
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Energietechnik , Maschinenbau
    Notizen: Abstract The thermal oxidative stability of various formulations based on emulsion-grade ABS was studied by the chemiluminescence technique. Emulsion products were found to be essentially less stable than ionic mass polymerization resins. Among the antioxidants studied, Santonox R is clearly more efficient than Irganox 1076 and Irganox 3114, and its superiority is reflected primarily in improved induction period values. The introduction of Tinuvin 770 and Tinuvin 328 UV stabilizers into emulsion resins does not change the durability of the products. In mixtures where both Irganox 1076 and UV stabilizers are present, a certain antagonistic effect was noted at high UV stabilizer concentrations.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02068674
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  • 16
    Digitale Medien
    Digitale Medien
    Effect of ionic interactions on the oxidation of Fe(II) with H2O2 in aqueous solutions (1991)
    Springer
    Journal of solution chemistry 20 (1991), S. 1079-1092 
    Details
    ISSN: 1572-8927
    Schlagwort(e): Fe(II) ; oxidation ; H2O2 ; ionic strength ; NaCl ; NaClO4
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The oxidation of Fe(II) with H2O2 has been measured in NaCl and NaClO4 solutions as a function of pH, temperature T (K) and ionic strength (M, mol-L−1). The rate constants, k (M−1-sec−1), d[Fe(II)]/DT=-k[Fe(II)][2O2] at pH=6.5 have been fitted to equations of the form log k = log k0+ AI 1/2+BI+CI 1/2/T Where log k0=15.53-3425/T in water; A=−2.3, −1.35; B=0.334, 0.180; and C=391, 235, respectively, for NaCl (σ=0.09) and NaClO4 (σ =0.08). Measurements made in NaCl solutions with added anions yield rates in the order B(OH) 4 − 〉HCO 3 − 〉ClO 4 − 〉Cl−〉NO 3 − 〉SO 4 2− and are attributed to the relative strength of the interactions of Fe2+ or FeOH+ with these anions. The FeB(OH) 4 + species is more reactive while the FeCO 3 0 , FeCl+, FeNO 3 + and FeSO 4 0 species are less reactive than the FeOH+ ion pair. The general trend is similar to our earlier studies of the oxidation of Fe(II) with O2 except for B(OH) 4 − . The effect of pH on the logk was found to be a quadratic function of the concentration of H+ or OH− from pH=4 to 8. These results have been attributed to the different rate constants for Fe2+ (k0) and FeOH+ (k1) which are related to the measured k by, k=k0αFe + k1αFeOH, where αi is the molar fraction of species i. The rates increase due to the greater reactivity of FeOH+ compared to Fe2+. k0 is independent of composition and ionic strength but k1 is a function of ionic strength and composition due to the interactions of FeOH+ with various anions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00649098
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  • 17
    Digitale Medien
    Digitale Medien
    Preparation and characterization of bimodal porous carbons derived from a styrene-divinylbenzene copolymer (1997)
    Springer
    Adsorption 3 (1997), S. 67-79 
    Details
    ISSN: 1572-8757
    Schlagwort(e): porous carbons ; activation ; oxidation ; surface oxygen groups ; LTPD
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Physik , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Abstract A styrene/divinylbenzene copolymer has been used as precursor for making porous carbons with bimodal pore size distributions (i.e., with both microporosity and mesoporosity). Pretreatment of the as-received copolymer by mild oxidation in air, significantly increased the carbon yield after carbonization. Reactivity studies of the polymer-based chars to CO2 clearly show the influences of some important factors such as carbonization temperature, heating rate, soak time on char reactivities. Bimodal porous carbons were prepared by carbonization of the preoxidized styrene/divinylbenzene copolymer in N2, followed by activation in CO2 at different temperatures to different levels of burnoff. The pore structures of the porous carbons produced have been characterized by various techniques such as gas adsorption and mercury porosimetry. The surfaces of the porous carbons produced, and a commercial carbon adsorbent, have been modified with HNO3 and H2O2 treatment at various conditions. Characterization of the surface oxygen functionality, both quantitatively and qualitatively, has been achieved using techniques such as Linear Temperature Programed Desorption (LTPD) and selective neutralization of bases.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01133008
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  • 18
    Digitale Medien
    Digitale Medien
    The Influence of Catalyst Composition on the Oxidation Process of Carbonado Type Synthesized Polycrystalline Diamonds (1997)
    Springer
    Advanced performance materials 4 (1997), S. 297-304 
    Details
    ISSN: 1572-8765
    Schlagwort(e): carbonado ; diamond ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The oxidation of carbonado type synthesized polycrystalline diamonds produced from graphite together with catalytic Ni-Mo alloy doped with TiB2 and BNcub was investigated. It was found that the addition of these boron compounds increases the oxidation resistance of the carbonado type synthesized polycrystalline diamonds. The oxidation mechanism acting on the carbonado type synthesized polycrystalline diamonds and the role of boron compounds in increasing the resistance to the oxygen reaction are discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008677105534
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  • 19
    Digitale Medien
    Digitale Medien
    Mechanism for the formation of carbon dioxide in the catalytic oxidation of carbon monoxide and methane on silica (1992)
    Springer
    Catalysis letters 13 (1992), S. 283-288 
    Details
    ISSN: 1572-879X
    Schlagwort(e): Silica ; oxidation ; methane ; carbon monoxide ; carbon dioxide ; labelled reaction
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The oxidation of carbon monoxide to carbon dioxide is shown to be catalyzed at 850 K or above over almost all lattice oxygen atoms on the surface of silica prepared by the sol-gel method from ethyl orthosilicate under conditions which yield high selectivity to carbon dioxide in the oxidation of methane.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00771001
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  • 20
    Digitale Medien
    Digitale Medien
    The partial oxidation of some cyclohexenes and branched chain olefins over a silver catalyst (1992)
    Springer
    Catalysis letters 16 (1992), S. 149-158 
    Details
    ISSN: 1572-879X
    Schlagwort(e): Silver ; oxidation ; cyclohexenes ; branched chain olefins
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The oxidation of some cyclic and branched chain olefins over a silver catalyst effective for the conversion of ethylene to ethylene oxide has been investigated in a steady state flow system. The reaction of cyclohexene produces benzene and that of both 1-methylcyclohexene and 4-methylcyclohexene yields toluene. The selectivity to aromatics exceeds 20% for fractional conversions below 0.2, but it can be improved to almost 50% by inclusion of an optimum quantity of dichloroethane in the feed. Styrene is oxidised more slowly than the cyclohexenes and only carbon dioxide and water are produced. The oxidation of 3,3-dimethyl-1-butene and 3-methyl-1-butene occurs much faster than that of the cyclic molecules and some of the corresponding epoxides are produced. The selectivity with the dimethyl-butene is 9–13% for conversions to 0.2. The methylbutene requires a higher temperature for reaction and the epoxide yield is lower. Factors influencing reactivity and product distribution are discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00764365
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  • 21
    Digitale Medien
    Digitale Medien
    Factors affecting bioleaching kinetics of sulfide ores using acidophilic micro-organisms (1999)
    Springer
    BioMetals 12 (1999), S. 1-10 
    Details
    ISSN: 1572-8773
    Schlagwort(e): acidophilic ; strain ; oxidation ; kinetics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: Abstract Recovery of metal values from sulfide ores by use of acidophilic microorganisms is gaining importance. A number of commercial/pilot plants are setup to find out the techno-economic feasibility of the overall process. The main drawback in the process is the slow kinetics of dissolution of metal values from the sulfide ores. To make the technology e attractive the kinetics should be improved considerably. There are various factors which determine the overall kinetics such as bacterial activity and concentration, iron and sulfur oxidation, oxygen consumption, reactor design and nature of ore. A brief review has been made dealing with the above parameters
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1009228210654
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  • 22
    Digitale Medien
    Digitale Medien
    The molecular structures and reactivity of V2O5/TiO2/SiO2 catalysts (1992)
    Springer
    Catalysis letters 13 (1992), S. 9-19 
    Details
    ISSN: 1572-879X
    Schlagwort(e): Vanadia ; titania ; silica ; Raman ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract A series of V2O5/TiO2/SiO2 catalysts were structurally investigated byin situ Raman spectroscopy and chemically probed by methanol oxidation in order to determine the molecular structure-reactivity relationships of the V2O5/TiO2/SiO2 catalysts. Only surface TiO x species are present on the 3% TiO2/SiO2 catalysts, and the surface TiO x species as well as bulk TiO2 (anatase) particles coexist on the 40% TiO2/SiO2 catalyst. The deposition of 1–3% vanadium oxide onto 3% TiO2/SiO2 and 4% vanadium oxide onto 40% TiO2/SiO2 forms only a surface vanadium oxide phase.In situ Raman studies reveal that the surface vanadium oxide species preferentially exist on the titania sites of the TiO2/SiO2 system. The interaction between the surface vanadia and the surface titania overlayer on SiO2 increases the methanol oxidation reactivity by two orders of magnitude relative to V2O5/SiO2. In the presence of bulk TiO2 (anatase) particles on the SiO7 support, the reactivity of the surface vanadia further increases by an order magnitude relative to the catalysts containing only surface titania, and is close to that of surface vanadia on bulk TiO2. This suggests that the surface VO x -TiO2 (bulk) interactions results in a more active site than the surface VO x -TiO x -SiO2 interactions. In addition, the V2O5/TiO2/SiO2 catalysts exhibit high selectivity towards HCHO because redox sites are predominant on the surface of these catalysts with essentially no acid site present.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00770942
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  • 23
    Digitale Medien
    Digitale Medien
    High yield synthesis of propanal from methane and air (1992)
    Springer
    Catalysis letters 13 (1992), S. 341-347 
    Details
    ISSN: 1572-879X
    Schlagwort(e): Methane ; oxidation ; oxidative coupling ; hydroformylation ; propanal ; catalysis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract High yield synthesis of propanal from methane and air can be obtained in a single pass at atmospheric pressure. Three catalytic processes are combined to give 13% yield of propanal based on total methane input. Ethene is made from the oxidative coupling reaction and carbon monoxide and hydrogen is generated from partial oxygenation of methane. These gases are combined and passed to a hydroformylation catalyst to give liquid propanal. The unreacted methane is inert in the hydroformylation stage, while oxygen deactivates the catalyst readily. The results imply that propanal can be obtained, in good yield, from methane and air provided that total oxygen conversion is achieved. The yield of propanal from the three combined processes can be substantially higher than that of ethene from the oxidative coupling reaction. Thus, higher yields of a condensible and oxygenated product are obtained.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00765036
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  • 24
    Digitale Medien
    Digitale Medien
    Selective oxidation of secondary amines over titanium silicalite molecular sieves, TS-1 and TS-2 (1996)
    Springer
    Catalysis letters 37 (1996), S. 213-216 
    Details
    ISSN: 1572-879X
    Schlagwort(e): titanium silicalites ; oxidation ; amines ; hydrogen peroxide
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Titanium silicalite molecular sieves, TS-1 and TS-2 having MFI and MEL structures, respectively, catalyze the oxidation of secondary amines to the corresponding hydroxylamines using hydrogen peroxide as the oxidant. Higher concentrations of H2O2 lead to further oxidation of hydroxylamine to nitrone. Diffuse reflectance spectroscopy shows the formation of a titanium peroxo complex upon addition of hydrogen peroxide to the TS-1 catalyst. The titanium peroxo complex oxidizes the substrate and reforms to a titanyl group.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00807756
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  • 25
    Digitale Medien
    Digitale Medien
    Transient experiments on the selective oxidation of methane to formaldehyde over V2O5/SiO2 studied in the temporal-analysis-of-products reactor (1993)
    Springer
    Catalysis letters 21 (1993), S. 209-214 
    Details
    ISSN: 1572-879X
    Schlagwort(e): Methane ; formaldehyde ; oxidation ; vanadium oxide ; silica
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Methane oxidation to formaldehyde was studied over a vanadium oxide catalyst supported on silica at 630 °C using the technique known as temporal analysis of products with sequential pulsing of methane and oxygen. This work shows that methane interacts very weakly and oxygen very strongly with the catalyst surface and it is concluded that the initial activation of methane involves an adsorbed oxygen species. Methyl radicals formed in the first step subsequently extract lattice oxygen to yield formaldehyde.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00769472
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  • 26
    Digitale Medien
    Digitale Medien
    Novel iron meso-nitrooctaethylporphine complexes for the catalytic reaction of alkanes with molecular oxygen (1994)
    Springer
    Catalysis letters 24 (1994), S. 79-83 
    Details
    ISSN: 1572-879X
    Schlagwort(e): Metallonitroporphines ; oxidation ; isobutane ; propane
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Introducing nitro groups into themeso-positions of a metalloporphyrin converts a catalytically inactive complex into a highly active catalyst for the oxidation of alkanes with molecular oxygen. The degree of nitration correlates with both the Fe(III)/Fe(II) reduction potential and the catalytic activity.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00807377
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  • 27
    Digitale Medien
    Digitale Medien
    Catalytic oxidation of cyclohexene with molecular oxygen by polyoxometalate-intercalated hydrotalcites (1996)
    Springer
    Catalysis letters 40 (1996), S. 43-45 
    Details
    ISSN: 1572-879X
    Schlagwort(e): oxidation ; cyclohexene ; polyoxometalate-intercalated hydrotalcite
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Cyclohexene was oxidized with molecular oxygen over transition-metal-substituted polyoxometalate-intercalated hydrotalcites to produce 2-cyclohexene-1-one and 2-cyclohexene-1-ol with high selectivity under mild reaction conditions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00807455
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  • 28
    Digitale Medien
    Digitale Medien
    A broad spectrum catalytic system for removal of toxic organics from water by deep oxidation using dioxygen as the oxidant (1996)
    Springer
    Catalysis letters 40 (1996), S. 95-99 
    Details
    ISSN: 1572-879X
    Schlagwort(e): palladium metal ; oxidation ; toxic organics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract In water, metallic palladium was found to catalyze the deep oxidation of a wide variety of functional organics by dioxygen at 80–90°C in the presence of carbon monoxide. Several classes of organic compounds were examined: benzene, phenol and substituted phenols, aliphatic and aromatic halogenated compounds, organophosphorus, and organosulfur compounds. In every case, deep oxidation to carbon monoxide, carbon dioxide, and water occurred in high yields, resulting in up to several hundred turnovers over a 24 h period. Since the heterogeneous catalyst can be removed by simple filtration, simultaneous water purification and contaminant destruction becomes feasible. For those substrates that are insoluble in pure water, a mixture of water and perfluorobutyric acid was successfully employed as the solvent.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00807463
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  • 29
    Digitale Medien
    Digitale Medien
    X-ray photoelectron spectroscopy of Pd/γ-alumina and Pd foil after catalytic methane oxidation (1995)
    Springer
    Catalysis letters 34 (1995), S. 31-40 
    Details
    ISSN: 1572-879X
    Schlagwort(e): palladium ; PdO ; alumina ; methane ; oxidation ; carbon ; XPS ; ellipsometry ; structure sensitivity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Samples of palladium supported onγ-alumina and a palladium foil were used as catalysts for methane oxidation at 550° C. The samples were quenched quickly in the reaction chamber to room temperature in flowing Ar and then transferred in vacuo for XPS analysis. Structure sensitivity was manifest from an increase in PdO stability and a decrease in carbon deposition relative to Pd with increasing particle size. The results were compared with recent ellipsometric data.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00808319
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  • 30
    Digitale Medien
    Digitale Medien
    Mo incorporation in MCM-41 type zeolite (1998)
    Springer
    Catalysis letters 52 (1998), S. 25-29 
    Details
    ISSN: 1572-879X
    Schlagwort(e): metallosilicate ; mesoporous ; MCM-41 ; Mo-MCM-41 ; catalysis ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Mo-incorporated MCM-41 has been prepared by direct hydrothermal synthesis. XRD and N2-adsorption measurements showed the characteristics of MCM-41. IR, FT-Raman and UV-VIS DR spectroscopic analyses gave the evidences for the incorporation of Mo in the framework of MCM-41. They are found to be stable and active for cyclohexanol and cyclohexane oxidation reactions with H2O2 as oxidant. Activity of this system has been compared with that of Ti-MCM-41 and molybdena impregnated on pure siliceous MCM-41.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1019019403375
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  • 31
    Digitale Medien
    Digitale Medien
    Surface acid property and its relation to SCR activity of phosphorus added to commercial V2O5(WO3)/TiO2 catalyst (1998)
    Springer
    Catalysis letters 53 (1998), S. 65-71 
    Details
    ISSN: 1572-879X
    Schlagwort(e): selective catalytic reduction ; nitric oxide reduction ; phosphorus ; acid property
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract To examine the influence of phosphorus on the commercial V2O5(WO3)/TiO2 SCR catalyst, measurements were carried out by means of infrared and Raman spectroscopy, XPS, and NO reduction measurement as a function of phosphorus loading. Phosphorus added to the catalyst was found to disperse well over the catalyst without a significant agglomeration up to 5 wt% P2O5 addition. The number of the hydroxyl groups bonded to the vanadium and titanium species decreased readily with increasing amount of phosphorus. Correspondingly, the hydroxyl groups bonded to the phosphorus species were formed. NH3 adsorbed on both hydroxyl groups bonded to vanadium and phosphorus as ammonium ions, implying that the P–OH groups formed are also responsible for the Brønsted acidity. The NO reduction activity was found to be decreased with increasing amount of phosphorus; however, the influence of phosphorus was relatively small irrespective of the large amount of phosphorus addition. The deactivation might be caused by the change in the nature of the surface hydroxyl groups as Brønsted acid sites. Phosphorus species might partially wrap the surface V=O and W=O groups, which might also contribute to the deactivation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1019020931117
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  • 32
    Digitale Medien
    Digitale Medien
    Alkene selectivity enhancement in the oxidation of propane on calcium-based catalysts (1999)
    Springer
    Catalysis letters 59 (1999), S. 67-72 
    Details
    ISSN: 1572-879X
    Schlagwort(e): propane ; oxidation ; calcium-based catalysts ; tetrachloromethane
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The oxidation of propane has been investigated in the presence and absence of tetrachloromethane (TCM) on calcium hydroxyapatite (CaHAp), Ca3(PO4)2, CaSO4 and CaO at 723 K. In the absence of TCM, the conversion of C3H8 on CaHAp was 7.7–9.2% during 6 h on-stream while that on Ca3(PO4)2, CaSO4 and CaO was 0.6, 0 and 0.2–0.4%, respectively. The principal products on all catalysts in the absence of TCM were CO and CO2 with small selectivities to C3H6 and C2H4 (both 5–6%) observed on CaHAp. Upon addition of TCM, the selectivity to C3H6 on all catalysts and the conversion of C3H8 on CaSO4 increased while, with increasing time-on-stream, the changes in the conversion and selectivity were dependent upon the nature of the catalysts. XPS and XRD analyses provide evidence for the presence of chlorine in the surface and/or bulk of three of the catalysts, suggesting that chlorinated species on the solids play a role in the selectivity enhancement, but the absence of chlorine from the sulphate demonstrates the dissimilarities of the catalysts in their abilities to sorb and decompose TCM.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1019091731368
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  • 33
    Digitale Medien
    Digitale Medien
    Synergistic effects in the oxidation of methane on strontium and lead hydroxyapatites (1999)
    Springer
    Catalysis letters 57 (1999), S. 161-165 
    Details
    ISSN: 1572-879X
    Schlagwort(e): methane ; oxidation ; strontium hydroxyapatite ; lead hydroxyapatite ; tetrachloromethane
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The oxidation of methane has been investigated on lead hydroxyapatite (PbHAp), strontium hydroxyapatite (SrHAp) and their binary mixtures at 873 K. PbHAp showed no activity for the oxidation of methane, while SrHAp produced carbon monoxide selectively at 2–4% conversion. On binary mixtures of the hydroxyapatites the conversion of methane and the selectivity to C2 compounds reached values higher than those of the separate constituents of the mixture. With tetrachloromethane in the feed stream a similar synergistic effect was observed with conversions of methane and selectivities to CH3Cl higher on the binary mixtures than those on either SrHAp or PbHAp. The strontium-containing hydroxyapatite appears to play a crucial role in the activation of methane, while the presence of the lead-containing analogue is apparently required for the minimization of undesirable processes involving methyl radicals.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1019024421857
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  • 34
    Digitale Medien
    Digitale Medien
    The partial oxidation of norbornene over a silver catalyst under steady state conditions (1991)
    Springer
    Catalysis letters 9 (1991), S. 133-143 
    Details
    ISSN: 1572-879X
    Schlagwort(e): Norbornene ; oxidation ; silver ; norbornene epoxide ; 3-cyclohexene-1-carboxyaldehyde
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The continuous oxidation of norbornene (C7H10) by molecular oxygen over a silver catalyst at 500–573 K has been investigated. In contrast to that observed during the temperature programmed reaction of norbornene and oxygen adsorbed on Ag(110) no norbornene epoxide is formed. Instead benzene is the sole partial oxidation product. A stable selectivity of 20 to 25% with fractional conversions up to 0.8 at 573 K could be obtained by inclusion of 15 to 30 ppm dichloroethane in the feed. Separate experiments withexo-norbornene epoxide showed that in the absence of oxygen it was almost completely isomerised to 3-cyclohexene-1-carboxyaldehyde with production of lesser amounts of norcamphor and norbornene. With oxygen present carbon dioxide and small amounts of benzene were also produced. It is concluded that norbornene epoxide cannot be a gas phase intermediate in the production of benzene from norbornene.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00769092
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  • 35
    Digitale Medien
    Digitale Medien
    Oxidation of acrolein on a multicomponent oxide catalyst (1992)
    Springer
    Catalysis letters 15 (1992), S. 401-404 
    Details
    ISSN: 1572-879X
    Schlagwort(e): Acrylic acid ; oxidation ; mixed oxides ; acrolein
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Catalytic oxidation of acrolein to acrylic acid has been studied and the optimum composition of the multicomponent catalyst Mo a V b Cu c Fe d O x has been found. The reaction kinetics has been measured.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00769164
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  • 36
    Digitale Medien
    Digitale Medien
    Silicoaluminophosphate number eighteen (SAPO-18): a new microporous solid acid catalyst (1994)
    Springer
    Catalysis letters 28 (1994), S. 241-248 
    Details
    ISSN: 1572-879X
    Schlagwort(e): coke ; zeolites ; catalyst regeneration ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract SAPO-18, which has a microporous framework structure related to, but crystallographically distinct from, that of the solid acid catalyst SAPO-34, was synthesized hydrothermally from a silicoaluminophosphate gel containing N,N-diisopropylethylamine as a structuredirecting template. Although both materials have similar Si/(Si + Al + P) ratios, the content of Brønsted acid sites in SAPO-18 is considerably less than that in SAPO-34. As catalysts for methanol conversion to light olefins, SAPO-18 and SAPO-34 have closely similar initial activity and selectivity, but the lifetime of SAPO-18 is distinctly superior to that of SAPO-34.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00806053
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  • 37
    Digitale Medien
    Digitale Medien
    Effect of fluorination of alumina support on activity of platinum catalysts for complete oxidation of benzene (1997)
    Springer
    Catalysis letters 49 (1997), S. 155-161 
    Details
    ISSN: 1572-879X
    Schlagwort(e): fluorination ; alumina ; platinum catalysts ; oxidation ; oxidation of benzene
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Platinum supported on fluorinated alumina is more active for the total oxidation of benzene than is the catalyst with the same Pt loading supported on hydrophilic unfluorinated alumina. The Pt-F/alumina catalyst contains well-dispersed small Pt particles, in contrast to Pt/alumina. The high dispersion is a consequence of a strong metal-support interaction.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1019065507551
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  • 38
    Digitale Medien
    Digitale Medien
    Fischer-Tropsch synthesis over iron catalysts (1990)
    Springer
    Catalysis letters 7 (1990), S. 241-251 
    Details
    ISSN: 1572-879X
    Schlagwort(e): Fischer-Tropsch synthesis ; iron based catalysts ; Fe ; Co ; Ru catalysts ; fixed bed reactors ; fluidized bed reactors ; sulfur poisoning ; oxidation ; coke fouling
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Because of the decreased profitability of making synthetic fuels, Sasol intends expanding its production of the higher valued chemicals, in particular waxes and olefins. The advantages and disadvantages of using Fe, Co and Ru catalysts are discussed from the point of view of costs, availability, product selectivity, activity and sensitivity to poisons. The loss of activity and selectivity of iron based catalysts in both fixed and fluidized bed reactors is discussed. The main contributing factors are sulfur poisoning, oxidation and coke fouling. In fixed bed reactors sulfur poisoning and “coke” laydown deactivates the front end of the bed while hydrothermal sintering/oxidation deactivates the back end. In fluidized beds the deposition of large amounts of Boudouard carbon doesnot markedly lower the activity. The smaller catalyst particles end up consisting of small iron carbide entities embedded in a matrix of carbon. The larger catalyst particles consist of cores of inert magnetite surrounded by the carbide/carbon matrix. FT reactor development at Sasol is briefly reviewed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00764506
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  • 39
    Digitale Medien
    Digitale Medien
    A new process for acetic acid production by direct oxidation of ethylene (1999)
    Springer
    Catalysis surveys from Japan 3 (1999), S. 55-60 
    Details
    ISSN: 1572-8803
    Schlagwort(e): acetic acid ; oxidation ; Pd ; heteropoly acid ; ethylene
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract A new process for acetic acid production by direct oxidation of ethylene which was established and commercialized is described. The catalyst system consisting of Pd and heteropoly acid exhibits excellent activity and selectivity. The addition of Se or Te to the catalyst system is effective to suppress the formation of carbon dioxide. This new process is applicable to a plant of a wide range of size corresponding to the local demand. Because this new process produces little waste water, it is very friendly to the environment.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1019003230537
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  • 40
    Digitale Medien
    Digitale Medien
    Oxidation and reduction effects of propane–oxygen on Pd–chlorine/alumina catalysts (2000)
    Springer
    Catalysis letters 64 (2000), S. 163-169 
    Details
    ISSN: 1572-879X
    Schlagwort(e): oxidation ; reduction of palladium catalysts ; chlorine effects
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Pd–chloride precursor salt was used to prepare Pd/Al2O3 catalysts. TPSR measurements showed three distinct reactions for the oxidation of propane on palladium surface under excess of hydrocarbon: complete oxidation, steam reforming and propane hydrogenolysis. Propane oxidation on palladium catalysts was related to the Pd2+ sites observed on Pd/Al2O3 through infrared of adsorbed carbon monoxide. In fresh catalysts reduced by H2, the IR spectra showed the linear and bridge adsorbed CO species on the Pd0 surface. After propane reaction, a new band at 2130 cm-1 related to CO adsorption on Pd2+ species was noted. Carbon monoxide species adsorbed on Pd0 were also observed in all samples after reaction. Our results suggest surface ratios of Pd0/PdO during the propane oxidation. On the other hand, time on stream conversions of the complete oxidation of propane were affected by either the water generated during the reaction or added as a reactant at 10 vol%. The water generated by the reaction helped to eliminate chlorine residues in the form of oxychloride species leading to an increasing of the activity. However, the presence of water into the reaction mixture caused a strong decreasing of the activity. The inhibition mechanism of propane oxidation in the presence of water consisted in the dissociative adsorption of water on palladium sites with the possible formation of palladium hydroxide (Pd–OH) at the surface, diminishing the number of active surface sites. Dynamic fluctuations into the reaction conditions supported the idea that a pseudo‐equilibrium adsorption–desorption of water was reached. After water removal or increasing in the reaction temperature the equilibrium was shifted to the direction of OH–Pd decomposition. This behavior suggests that the inhibitory effect of water is a reversible phenomenon, being a function of the amount of water and the reaction temperature.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1019034903453
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  • 41
    Digitale Medien
    Digitale Medien
    Preparation of Polyuronic Acid from Cellulose by TEMPO-mediated Oxidation (1998)
    Springer
    Cellulose 5 (1998), S. 153-164 
    Details
    ISSN: 1572-882X
    Schlagwort(e): cellulose ; TEMPO ; polyglucuronic acid ; degree of polymerization ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Abstract Various cellulose samples were oxidized by 2,2,6,6,-tetramethylpipelidine-1-oxyl radical (TEMPO)-NaBr-NaClO systems, and the effects of oxidation conditions on chemical structures and degrees of polymerization of the products obtained were studied. In the case of regenerated and mercerized celluloses, almost all C6 primary alcohol groups were selectively oxidized to carboxyl groups, and water-soluble polyglucuronic acid (cellouronic acid) sodium salts were obtained almost quantitatively; the degrees of polymerization were influenced greatly by the amount of TEMPO added, and the oxidation time and temperatures. Cellouronic acids prepared from mercerized linter and kraft pulps had size exclusion chromatograms with two separate peaks due to higher and lower molecular weight fractions. On the other hand, only small amounts of carboxyl groups were introduced into native cellulose samples. Since polyglucuronic acids prepared from cellulose by the TEMPO–NaBr– NaClO systems regularly consist of the glucuronic acid repeating unit, differing from the conventional water-soluble cellulose derivatives, they may open new fields of cellulose utilization.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1009208603673
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  • 42
    Digitale Medien
    Digitale Medien
    Preparation of metallosilicates with zeolite structure by atom-planting method (1998)
    Springer
    Catalysis surveys from Japan 2 (1998), S. 121-132 
    Details
    ISSN: 1572-8803
    Schlagwort(e): zeolite ; metallosilicate ; atom-planting ; modification ; catalysis ; acidity ; shape-selective alkylation ; oxidation ; hydrogen peroxide
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Atom-planting, a useful method to prepare some metallosilicates having zeolitic structure, was proposed. By treatment of highly siliceous zeolite with metal chloride vapor at selected temperature, metal cation could be introduced into the defect sites (hydroxyl nests) of zeolite framework. By the atom-planting method, some metallosilicates which are difficult to be synthesized by hydrothermal synthesis could be prepared. The vapor phase shape-selective alkylation of ethylbenzene with ethanol, and the liquid phase selective oxidation with hydrogen peroxide on the metallosilicates prepared by atom-planting method were reviewed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1019034610065
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  • 43
    Digitale Medien
    Digitale Medien
    Steady-state conversion of methane to C4+ aliphatic products in high yields using an integrated recycle reactor system (2000)
    Springer
    Catalysis letters 66 (2000), S. 1-4 
    Details
    ISSN: 1572-879X
    Schlagwort(e): methane ; oxidation ; aliphatic hydrocarbons ; zeolite ; recycle reactor
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Conversion of methane in high yields to C4+ nonaromatic hydrocarbons was demonstrated in a recycle system. The principal components of the recycle system included an oxidative coupling reactor with a Mn/Na2WO4/SiO2 catalyst at 800°C for conversion of methane to ethylene, and a reactor with an H-ZSM-5 zeolite at 275°C for subsequent conversion of ethylene to higher hydrocarbons. Total yields of C4+ products were in the range of 60–80%, and yields of C4+ nonaromatic hydrocarbons were in the range of 50–60%.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1019039321142
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  • 44
    Digitale Medien
    Digitale Medien
    Benzylacetate synthesis by oxyacetoxylation of toluene on Pd–Bi binary catalyst (2000)
    Springer
    Topics in catalysis 13 (2000), S. 243-248 
    Details
    ISSN: 1572-9028
    Schlagwort(e): oxidation ; oxyacetoxylation ; alloy ; palladium ; bismuth ; benzylacetate
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Benzylacetate synthesis from toluene, acetic acid and oxygen on Pd–Bi binary catalyst was studied in the liquid phase. By incorporation of Bi with Pd, both the activity and selectivity were improved. Especially better stability was obtained with the catalyst having Pd/Bi = 3. Deactivation of the catalyst was investigated in detail by XRD, XPS, TEM, elemental analysis, EPMA and so on. Comparing the used catalyst with the fresh one, it was indicated that the main cause of deactivation was the dissolution of Pd into the reaction mixture from the most outer surface of the catalyst. By adopting proper reaction conditions to prevent the Pd dissolution, the catalyst having Pd/Bi = 3 was suggested to be used as an industrial catalyst.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1009026131545
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  • 45
    Digitale Medien
    Digitale Medien
    The chemisorption of nitric oxide and the oxidation of ammonia at Cu(110) surfaces: a X-ray photoelectron spectroscopy (XPS) and scanning tunnelling microscopy (STM) study (2000)
    Springer
    Topics in catalysis 14 (2000), S. 101-109 
    Details
    ISSN: 1572-9028
    Schlagwort(e): nitric oxide ; ammonia ; oxidation ; X-ray photoelectron spectroscopy ; scanning tunnelling microscopy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The dissociative chemisorption of nitric oxide at Cu(110) has been shown to result in rapid ordering of oxygen adatoms as (2×1)O chains oriented along the 〈100〉 direction while the associated nitrogen adatoms are mainly disordered at 295 K. Surface diffusion of the N adatoms, following bond cleavage, is activated and ordering of the (2×3)N strings occurs on heating to 430 K. A number of distinct reaction pathways have been isolated during the oxidation of ammonia resulting in the formation of either chemisorbed imide or nitrogen adatoms. The latter depending on temperature, may exhibit a (2×3)N, a (3×3)N or both structures may exist simultaneously. The concentration of nitrogen in the complete (2×3)N structure has been determined to be 6.6×1014 cm-2, with only a 25% decrease in nitrogen concentration leading to the transformation to the (3×3)N structure. The oxygen atoms at a Cu(110)–O overlayer, and present at the ends of the (2×1) strings terminating in steps, show specific reactivity when exposed to ammonia at 375 K resulting in the “decoration” of the steps with imide species while the oxygens within the (2×1) strings remain unreactive.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1009015318393
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  • 46
    Digitale Medien
    Digitale Medien
    Direct liquid‐phase side‐chain oxidation of alkylbenzenes over 2 catalyst (2000)
    Springer
    Catalysis letters 65 (2000), S. 181-183 
    Details
    ISSN: 1572-879X
    Schlagwort(e): alkylbenzene ; toluene ; ethylbenzene ; xylene ; mesitylene ; p‐ethyltoluene ; cumene ; p‐cymene ; oxidation ; palladium ; 1,10‐phenanthroline
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Only the side‐chain oxidation of alkylbenzenes (R–C6H3–R′–R″ R=H, Me, Et, Pri R′=H, Me; and R″=H, Me) by oxygen (35–50 atm, 200)C° is promoted in the presence of [Pd(phen)(OAc)2].
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1019094011147
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  • 47
    Digitale Medien
    Digitale Medien
    Catalysis by porous heteropoly compounds (1998)
    Springer
    Catalysis surveys from Japan 2 (1998), S. 31-44 
    Details
    ISSN: 1572-8803
    Schlagwort(e): porous heteropoly compounds ; Pt-promoted heteropoly compounds ; shape selectivity ; water-tolerant catalyst ; hydrogenation ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract This paper attempts to review recent works on catalysis of porous heteropoly compounds. The salts of heteropolyacids having Keggin structure with large cations like Cs+ are porous materials. For Cs hydrogen salts, the pore width can be controlled by the Cs content. Cs2.5H0.5PW12O40 has the largest amount of protons on the surface among the acidic Cs salts and possesses pores with bimodal distribution in the micro and meso region. Efficient performances were demonstrated for acid-catalyzed reactions such as skeletal isomerization of η-butane in solid-gas system, alkylation and acylation in solid-liquid system, and hydrolysis and hydration in solid-water system. A microporous salt, Cs2.2H0.8PW12O40, exhibited reactant shape selectivity towards direct decomposition of esters. Furthermore, an ultramicroporous bifunctional catalyst, Pt–Cs2.1H0.9PW12O40 of which the pore width is around 5 Å, exhibits reactant shape selectivity for hydrogenation of alkenes and oxidation of hydrocarbons, and product shape selectivity for skeletal isomerization of η-butane.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1019053719634
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  • 48
    Digitale Medien
    Digitale Medien
    The structural basis for the enhanced oxygenase activity of copper acetate dimers encapsulated in zeolites (2000)
    Springer
    Topics in catalysis 11-12 (2000), S. 359-367 
    Details
    ISSN: 1572-9028
    Schlagwort(e): zeozyme ; encapsulated complexes ; copper acetate ; copper dimers ; enzyme mimic ; EPR of copper ; tyrosinase ; oxidation ; oxygenase ; tyrosine oxidation ; phenol oxidation ; hydroxylation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The oxygenase mimicking activity of copper acetate dimers in the regioselective ortho-hydroxylation of L-tyrosine to L-dopa is enhanced on encapsulation in zeolite Y. The structure and magnetic properties of the catalytic active site were characterized by EPR spectroscopy. The spectra of this “zeozyme” reveal the presence of (1) copper acetate dimers in the supercages and (2) isolated Cu(II) ions in the sodalite cages of the zeolite. There are significant differences in the EPR spectra of the “neat” and encapsulated complexes: on encapsulation in zeolite, the Cu–Cu exchange coupling constant, −, increases to 310 from 259 cm−1 for the “neat” complex (i.e., by about 19.7%). Simultaneously the Cu–Cu separation in the dimer, estimated indirectly from the exchange coupling constant, shortens to 2.40 Å in the encapsulated state from 2.64 Å in the “neat” complex. There is, hence, a relatively greater overlap of the metal orbitals of the dimer copper atoms inside the restricted confines of the zeolite cages. The consequent, enhanced, trans axial lability of the phenolate and dioxygen ligands promotes the catalytic oxygenase activity of copper acetate dimers on encapsulation in zeolites. A causal relationship between changes in the structural features of an active site on encapsulation in the zeolite and the corresponding catalytic activity has, thus, been established.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1027277831603
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  • 49
    Digitale Medien
    Digitale Medien
    The ecosystem of a mesotrophic lake-II. Interactions among nutrient load, river flow, and epilimnion depth (1991)
    Springer
    Aquatic sciences 53 (1991), S. 263-272 
    Details
    ISSN: 1420-9055
    Schlagwort(e): Lake ecosystem ; chl-a ; phosphorus ; nitrogen ; river flow ; thermocline ; simulation model ; multiple regression
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The management variables which primarily affect phytoplankton biomass (as chl-a) in Lake Mjøsa, Norway, are total phosphorus loading (TP) and the timing and volume of water through flow (by active storage reservoirs). The response of the lake to changes in these factors is studied using a simulation model of the lake ecosystem. Chl-a responses from both observed data and the simulated results are extracted by multiple regression. Results show that decreasing TP load decreases chl-a, but less at low TP levels (〈 10 mg TP · m−3). There is also a certain time period for peak river flow which gives the least yield of chl-a per unit TP. This time period occurs in early summer (i.e., around June 10) if the total phosphorus load is low, and later if the load is high. Both observations and simulation results show that a high water flow increases chl-a at low epilimnion depths (〈 15 m), but that the same high water flow decreases chl-a when epilmnion is deep.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00877062
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  • 50
    Digitale Medien
    Digitale Medien
    The short term response to eutrophication abatement (1990)
    Springer
    Aquatic sciences 52 (1990), S. 199-220 
    Details
    ISSN: 1420-9055
    Schlagwort(e): Eutrophication ; lake management ; phosphorus ; ecosystem ; chlorophyll-a ; mathematical modelling
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract We compare results of a new model for predicting the short term inter annual changes in chlorophyll-a (chl-a) in lakes after reductions in total phosphorus (TP) to predictions made by least squares regression models. In the new method, slopes of chl-a/TP graphs (both axes in mg · m−3) are depicted in frequency diagrams and used to extract information on the expected, short term chl-a/TP response. The short term response for nine shallow (〈 10 m deep) and nutrient rich lakes to changes in TP was found to be: Chl-a = 0.49 · TP + 17.3, and for nine deep, P-limited lakes: Chl-a = 0.08 · TP + 3.5. If the TP-reduction is known to be greater than 10 mg · m−3, the expected slope increases to 0.58 for shallow lakes and to 0.26 for deep lakes. The slope, 0.58, is 8% lower than the slope for the long term response calculated by regression for the shallow lakes. For deep lakes the slope, 0.26, is 2 to 3 times higher than that calculated by regression, indicating that reductions in TP for deep lakes give greater effects than least squares regression equations suggest. We have also calculated the reduction in TP which will give about 80% probability that a reduction in chl-a will be observed next year. For shallow, P-limited lakes this reduction is about 30 mg · m−3 (5% of average initial in-lake TP concentration), and for deep lakes about 14 mg · m−3 (35% of average initial in-lake TP concentration).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00877280
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  • 51
    Digitale Medien
    Digitale Medien
    Vertical mixing in Überlinger See, western part of Lake Constance (1990)
    Springer
    Aquatic sciences 52 (1990), S. 256-268 
    Details
    ISSN: 1420-9055
    Schlagwort(e): Vertical mixing ; stratification ; phosphorus ; Lake Constance
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Depth variable vertical eddy diffusion coefficients for heat (K z) were calculated from continuously measured temperature profiles in Überlinger See (western part of Lake Constance). The temperatures were averaged over vertical intervals of 10 m yielding 14 discrete values (maximum depth of Überlinger See: 147 m). A linear fit from 10 June to 29 September 1987 was used to smooth the significant temperature fluctuations caused by internal seiches of Lake Constance. Assuming horizontal homogeneity for the smoothed data the Gradient-Flux-Method was applied to compute vertical diffusion coefficientsK z at different depths using the depth variable volumes and surfaces of the 14 layers. The resulting mean diffusion coefficients for the period from June to September are 0.04 cm2/s near the thermocline and up to 0.8 cm2/s in deeper strata (accuracy: ± 50%). It is shown that horizontal mixing between Überlinger See and Obersee (main lake) alters the computation ofK z by less than 50%. A relationship betweenK z and stability (Brunt-Väisälä) frequencyN is found which corresponds well to the theory of internal wave induced turbulence. Combining the diffusion coefficients with measured phosphorus profiles, a phosphorus flux from the hypolimnion to the epilimnion of (0.7 ± 0.4) mg P m−2 d−1 was calculated, corresponding to about 20% of the average external loading per area of Lake Constance in 1986.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00877283
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  • 52
    Digitale Medien
    Digitale Medien
    Measurement of total dissolved phosphorus in small volumes of iron rich interstitial water (1992)
    Springer
    Aquatic sciences 54 (1992), S. 1-9 
    Details
    ISSN: 1420-9055
    Schlagwort(e): Sediment ; interstitial water ; phosphorus ; iron ; persulfate digestion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract It is shown that sorption of orthophosphate to iron compounds, formed during persulfate digestion, can cause a significant underestimation of total dissolved phosphorus in interstitial waters rich in iron and poor in phosphorus. Labelling the samples with carrier free32PO4 before digestion allows to correct for these losses.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00877261
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  • 53
    Digitale Medien
    Digitale Medien
    The effect of oxide structure and cation reduction potential of vanadates on the selective oxidative dehydrogenation of butane and propane (1992)
    Springer
    Catalysis letters 12 (1992), S. 45-50 
    Details
    ISSN: 1572-879X
    Schlagwort(e): Propane ; butane ; alkane ; oxidation ; dehydrogenation ; vanadates ; cation reduction potential ; oxide structure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The oxidative dehydrogenation of butane over a series of orthovanadates of cations of different reduction potentials showed a correlation that the selectivity for dehydrogenation decreased with increasing ease of reduction of the cation. The highest selectivity was observed on Mg orthovanadate. Mg pyrovanadate was nonselective for butane oxidation, but was as selective as Mg orthovanadate in propane oxidation. These results were interpreted by the different structures of the two Mg vanadates.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00767187
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  • 54
    Digitale Medien
    Digitale Medien
    The ozone sensitized oxidative conversion of methane to methanol and ethane to ethanol (1992)
    Springer
    Catalysis letters 16 (1992), S. 217-221 
    Details
    ISSN: 1572-879X
    Schlagwort(e): Methane ; ethane ; methanol ; ethanol ; ozone ; oxygen atom ; oxidation ; sensitization
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The reaction of O2, O3, and CH4 or C2H6 of 7.76, 0.24 and 92% of the hydrocarbon respectively (residence time of 8.8 min) at 1 atm, and 400 °C for CH4 and 300 °C for C2H6 gave CO, CO2, H2O, CH2O and CH3OH from CH4 and in addition CH4, C2H4, CH3CHO and C2H5OH from C2H6. No reaction occurred when O3 was absent indicating that the partial oxidation was sensitized (initiated) by the oxygen atoms formed by the decomposition of ozone.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00764374
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  • 55
    Digitale Medien
    Digitale Medien
    The influence of sulfur dioxide on propane oxidation activity over supported platinum and palladium (1994)
    Springer
    Catalysis letters 30 (1994), S. 41-51 
    Details
    ISSN: 1572-879X
    Schlagwort(e): propane ; oxidation ; platinum ; palladium ; sulfur dioxide ; alumina ; zirconia ; activity ; acidity ; kinetics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Earlier studies have shown that sulfur dioxide and metal-support interaction can strongly influence propane oxidation over platinum. In particular, oxidation activity is enhanced when platinum is supported on sulfated γ-alumina or zirconia compared to γ-alumina. Therefore, it is of interest to compare the performance of palladium under the same experimental conditions. Four model catalysts were examined: Pt/γ-alumina, Pt/zirconia, Pd/γ-alumina and Pd/zirconia. The metal loading was kept at or below 0.05 wt% to emphasize changes in activity attributable to metal-support interaction. Reaction rates were measured with and without sulfur dioxide. Surface sulfation was analyzed by measuring acid strength and evaluating spectra obtained by Fourier-transform infrared spectroscopy. In contrast to platinum, sulfation does not promote propane oxidation on Pd/γ-alumina, and Pd/zirconia is less active than Pd/γ-alumina.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00813671
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  • 56
    Digitale Medien
    Digitale Medien
    Multiple steady-states for the oxidation of aqueous ethanol with oxygen on a carbon supported platinum catalyst (1994)
    Springer
    Catalysis letters 30 (1994), S. 269-277 
    Details
    ISSN: 1572-879X
    Schlagwort(e): aqueous ethanol ; multiple steady-state ; oxidation ; platinum
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The selective oxidation of aqueous ethanol by dioxygen over a platinum on carbon catalyst was investigated in a three-phase continuously stirred tank reactor at a total pressure of 600 kPa, a temperature of 323 K, a pH of 8.4, and a catalyst concentration of 2.3 kg m−3. Multiple steady-states were obtained by systematic changes in the start-up procedure and variation of the feed concentration of ethanol and partial oxygen pressure in the reactor. The ethanol feed concentration was varied from 100 to 2500 mol m−3 and the partial oxygen pressure from 8 to 120 kPa. On the time scale of the experiments, i.e. 21 ks, two steady-states of the net disappearance rate of ethanol are observed in the ethanol feed concentration range from 500 to 2500 mol m−3 at a partial oxygen pressure of 58 kPa and in the range of partial pressure of oxygen from 8 to 120 kPa at an ethanol feed concentration of 500 mol m−3. Three steady-states are observed in the feed ethanol concentration range from 200 to 400 mol m−3 and a partial oxygen pressure of 58 kPa.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00813693
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  • 57
    Digitale Medien
    Digitale Medien
    Photocatalytic oxidation of substituted toluenes with irradiated TiO2 semiconductor. Effect of zeolite (1995)
    Springer
    Catalysis letters 33 (1995), S. 395-400 
    Details
    ISSN: 1572-879X
    Schlagwort(e): TiO2 ; heterogeneous photocatalysis ; oxidation ; substituted toluenes ; zeolites
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Photocatalytic oxidation of substituted toluenes was investigated on irradiated TiO2 and TiO2 combined with HY15 and HY20 zeolites. In all cases the oxidation occurred in the first step exclusively on either one substituent or the other, but never on both simultaneously. In the presence of a zeolite, photooxidation conversion was higher than that obtained without zeolite.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00814241
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  • 58
    Digitale Medien
    Digitale Medien
    Study of the deactivation mechanism of Al2O3-supported cobalt Fischer-Tropsch catalysts (1995)
    Springer
    Catalysis letters 34 (1995), S. 269-284 
    Details
    ISSN: 1572-879X
    Schlagwort(e): Fischer-Tropsch synthesis ; cobalt catalysts ; deactivation ; oxidation ; reduction ; promoters ; rhenium
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The influence of water on alumina-supported cobalt catalysts has been studied. The deactivation of supported Co catalysts was studied in a fixed-bed reactor using synthesis gas feeds containing different concentrations of water vapour. Supporting model studies were carried out using H2O/H2 feeds in conjunction with XPS and gravimetry. Rapid deactivation occurs on Re-promoted CO/Al2O3 catalysts when H2/CO/H2O feeds are used, whereas unpromoted CO/Al2O3 shows more stable activity. The results from the gravimetric studies suggest that only a small fraction of the bulk cobalt metal initially present reoxidizes to cobalt oxide during reaction. However, the XPS results indicate significant reoxidation of surface cobalt atoms or highly dispersed cobalt phases, which is likely to be the cause of the observed deactivation. Rhenium is shown to have a marked effect on the extent of reoxidation of alumina-supported cobalt catalysts.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00806876
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  • 59
    Digitale Medien
    Digitale Medien
    Oxidative dehydrogenation of ethane over La1−xSrxFeO3−δ perovskite oxides (1996)
    Springer
    Catalysis letters 38 (1996), S. 189-195 
    Details
    ISSN: 1572-879X
    Schlagwort(e): perovskite ; La1−xSrxFeO3−δ ; dehydrogenation ; oxidation ; ethane
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Catalysts of the composition La1−xSrxFeO3−δ, 0⩽x ⩽1, have been tested for the oxidative dehydrogenation of ethane in the temperature range 300–800°C. The catalyst is active above 400°C, giving a maximum yield of 37% ethylene at 650°C. Above 650°C, synthesis gas was formed together with methane, suggesting that the reforming reaction and thermal cracking of ethane took place. The catalytic data are compared to conductivity measurements on the same material, and a good correlation between the activity and p-type conductivity has been found. In the phase diagram for the system LaFeO3-SrFeO3−δ, a phase separation to two types of (La, Sr)FeO3−δ perovskites was observed in the La/Sr binary composition in the temperature range below 800°C. The phase separation can elucidate the dependency of the catalytic activity on its p-type conductivity.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00806567
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  • 60
    Digitale Medien
    Digitale Medien
    Inhibition of CO oxidation on hydroxyapatite by tetrachloromethane (1996)
    Springer
    Catalysis letters 39 (1996), S. 205-208 
    Details
    ISSN: 1572-879X
    Schlagwort(e): oxidation ; hydroxyapatite ; carbon monoxide ; inhibition ; tetrachloromethane
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The introduction of tetrachloromethane (TCM) into the feedstream of CO and O2 inhibits the formation of CO2 on hydroxyapatite. TCM interacts with the surface of hydroxyapatite to form its chlorinated analogue, chlorapatite, which suppresses the oxidation of CO to CO2. Thus, in the oxidative coupling of methane the beneficial effects of the addition of TCM to the feedstream result, at least in part, from the suppression of the further oxidation of CO.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00805584
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  • 61
    Digitale Medien
    Digitale Medien
    Oxidation of Cl-modified Ag(111) under UHV conditions and ethylene adsorption on the oxidized surface (1994)
    Springer
    Catalysis letters 26 (1994), S. 109-121 
    Details
    ISSN: 1572-879X
    Schlagwort(e): Cl-modified Ag(111) ; oxidation ; phonons ; ethylene adsorption
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Oxidation of Cl-modified Ag(111) under UHV conditions was investigated using AES, ISS and HREELS. The results showed that Cl-modified Ag(111) can be easily oxidized at 550 K by 1 × 10−6 mbar oxygen which was also heated to 550 K. With HREELS two fundamental vibrations at 600 and 1000 cm−1 were detected for silver oxide and the multiple losses and combination excitations as well. Ethylene adsorption on the oxide was analyzed by HREELS. Surface hydroxyl species was formed at 230 K and stable to above 300 K, which is attributed to silver oxide. Ethylidyne was suggested to form concurrently with hydroxyl species.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00824037
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  • 62
    Digitale Medien
    Digitale Medien
    Pyrene oxidation as a model reaction for characterizing the mechanism of coke oxidation on Y zeolites (1994)
    Springer
    Catalysis letters 28 (1994), S. 53-59 
    Details
    ISSN: 1572-879X
    Schlagwort(e): coke ; zeolites ; catalyst regeneration ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The same effect of temperature on the production of CO, CO2 and H2O was found during oxidative treatment of HY zeolites either impregnated with pyrene or coked. Therefore, pyrene oxidation can be used to specify the mechanism of coke oxidation. Three types of reactions can be distinguished: (a) condensation of polyaromatic molecules, (b) oxidation of polyaromatics into aldehydes, ketones, acids and anhydrides and (c) decarbonylation or decarboxylation of oxygenated compounds, all these reactions involving protonic sites.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00812469
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  • 63
    Digitale Medien
    Digitale Medien
    Platinum deactivation: in situ EXAFS during aqueous alcohol oxidation reaction (1998)
    Springer
    Catalysis letters 55 (1998), S. 141-145 
    Details
    ISSN: 1572-879X
    Schlagwort(e): platinum ; EXAFS ; catalysis ; catalyst deactivation ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract With a new set‐up for in situ EXAFS spectroscopy the state of a carbon‐supported platinum catalyst during aqueous alcohol oxidation has been observed. The catalyst deactivation during platinum‐catalysed cyclohexanol oxidation is caused by platinum surface oxide formation. The detected Pt–O co‐ordination at 2.10 Å during exposure to nitrogen‐saturated cyclohexanol solution is different from what is observed for the pure oxidised platinum surface (2.06 Å).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1019007601442
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  • 64
    Digitale Medien
    Digitale Medien
    Insights into surface reactivity: formic acid oxidation on Cu(110) studied using STM and a molecular beam reactor (1998)
    Springer
    Catalysis letters 56 (1998), S. 77-83 
    Details
    ISSN: 1572-879X
    Schlagwort(e): catalysis ; combustion ; oxidation ; formic acid ; STM ; molecular beams ; surface diffusion ; surface reactivity ; active sites ; reconstruction
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Using a combination of STM and molecular beam reactor data we summarise some important features of a model reaction (formic acid oxidation on Cu(110)) which is of general significance to surface reactivity and to catalysis. Three such features are highlighted here. The first concerns the role of weakly held species (possibly physisorbed) in surface reactions. These species, although of very short lifetime on the surface, can, nevertheless, diffuse over long distances to “find” a sparse distribution of active sites. Thus a very low coverage of oxygen on the surface of Cu(110) increases the sticking probability of all the formic acid molecules which strike the surface to high value (0.82), even though the clean surface is relatively unreactive. The important concept here is the “diffusion circle” or “collection zone” which represents the area of surface visited by the molecule in its short sojourn in the weakly held state. The second theme concerns the concept of the “flexible surface”. We show that the involvement of surface atoms in reactions directs the structure and reactivity for a particular reaction. For formic acid oxidation the liberation of Cu atoms during the removal of oxygen as water leads to gross restructuring of the surface and can lead to “compression” of one reactant (the oxygen in this case) into a lower area, higher local coverage, unreactive state (the c(6×2) oxygen structure). Thirdly, and finally, it is proposed that, for many surface reactions, the surface acts in an analogous way to a solvent, supporting a “dissolved” (highly mobile and fluxional) phase of intermediates at low coverage, which crystallise out above a critical coverage (the 2D “solubility limit”).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1019021431910
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  • 65
    Digitale Medien
    Digitale Medien
    A study of “superacidic” MoO3/ZrO2 catalysts for methane oxidation (1999)
    Springer
    Catalysis letters 57 (1999), S. 109-113 
    Details
    ISSN: 1572-879X
    Schlagwort(e): superacid ; zirconia ; molybdenum oxide ; methane ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract A series of zirconia-supported molybdenum oxide catalysts with different molybdenum loadings prepared using conditions reported to generate “superacidity” have been evaluated for their performance as catalysts for methane oxidation. A marked dependence of Mo content on activity has been observed, with the most active material being that with intermediate molybdenum content. 5 wt% MoO3/ZrO2 compares favourably with ZrxCe1-xO2 for methane combustion. The presence of MoO3 is observed to stabilise the tetragonal polymorph of ZrO2 and, as Mo content is increased, dispersed MoO3 crystallites are formed as evidenced by Raman spectroscopy. Temperature-programmed reduction studies evidence differences in the reduction behaviour of the materials as a function of loading. The results indicate that molybdenum oxide supported on monoclinic zirconia gives rise to the most active catalyst. It is tentatively suggested that the formation of a MoO3 monolayer during reaction may be of importance.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1019047632335
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  • 66
    Digitale Medien
    Digitale Medien
    Partial oxidation of methane to synthesis gas (1990)
    Springer
    Catalysis letters 6 (1990), S. 181-186 
    Details
    ISSN: 1572-879X
    Schlagwort(e): Metals for catalysis “syngas” ; oxidation ; nickel ; platinum group metals
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Partial oxidation of methane to synthesis gas has been carried out over a number of transition metal catalysts under a range of conditions. It is found that the metals Ni, Ru, Rh, Pd, Ir and Pt, either supported on alumina or present in mixed metal oxide precursors, will bring the system to equilibrium. The yield of CO and H2 improves with increasing temperature in the range 650–1050 K, and decreases with increasing pressure between 1 and 20 atm. An excellent yield (∼92%) is obtained with a 4∶2∶1 N2∶CH4∶O2 ratio at 1050 K and atmospheric pressure, with a space velocity of 4×104 hour−1.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00774718
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  • 67
    Digitale Medien
    Digitale Medien
    Formation of a liquid film of AgNO3 on a silver surface (2000)
    Springer
    Catalysis letters 64 (2000), S. 113-118 
    Details
    ISSN: 1572-879X
    Schlagwort(e): X‐ray photoelectron spectroscopy (XPS) ; scanning electron microscopy (SEM) ; silver ; oxidation ; surface chemical reaction ; NO ; NO x
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The behavior of a AgNO3/Ag2O/Ag “sandwich” upon heating in vacuum was studied by in situ X‐ray photoelectron spectroscopy (XPS) and ex situ scanning electron microscopy (SEM). The AgNO3/Ag2O/Ag “sandwich” was prepared by exposure of a silver foil to a NO : O2 mixture. The upper layer of the “sandwich” consists of AgNO3 crystals of a mean size between 0.1 and 0.4 μm. Heating at 550 K in vacuum results in melting of the AgNO3 crystals. A liquid film of AgNO3, readily wetting the silver, covers the surface. Cooling below the melting point of AgNO3 leads to the agglomeration of silver nitrate to long islands with a size reaching a few tens of micrometers (μm). The possible effects of AgNO3 liquid‐phase formation on surface processes are discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1019015826651
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  • 68
    Digitale Medien
    Digitale Medien
    Effect of the catalyst supports on the removal of perchloroethylene (PCE) over chromium oxide catalysts (2000)
    Springer
    Catalysis letters 64 (2000), S. 201-207 
    Details
    ISSN: 1572-879X
    Schlagwort(e): chlorinated hydrocarbons ; chromia ; titania ; alumina ; CVOCs ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The oxidation of perchloroethylene (PCE) was investigated over chromium oxide catalysts supported on TiO2, Al2O3, SiO2, SiO2–Al2O3 and activated carbon. The phase of chromium oxide on the catalyst surface is critical for the oxidation of PCE. The catalytic activity of PCE removal enhances as the formation of Cr(VI) species on the catalyst surface increases. The surface area and the type of the catalyst supports were also essential for high performance in the PCE oxidation. In addition, the structure of Cr(VI) on the catalyst surface also plays an important role for the decomposition of PCE. The polymerized Cr(VI) mainly formed by the interaction of metals with the support is the active reaction site for the present reaction system. CrOx/TiO2 reveals the strongest PCE removal activity among the catalysts examined in the present study.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1019076112539
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  • 69
    Digitale Medien
    Digitale Medien
    Effects of SO2 on the alkane activity of three-way catalysts (1991)
    Springer
    Catalysis letters 11 (1991), S. 183-190 
    Details
    ISSN: 1572-879X
    Schlagwort(e): Three-way catalysts ; sulphur dioxide ; poisoning ; promotion ; oxidation ; steam reforming
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Over current Pt-Rh/CeO2-Al2O3 catalysts, the conversion of alkanes occurs by two principal mechanisms: direct oxidation (HC + O2) and steam reforming (HC+H2O). Sulphur dioxide can influence both these mechanisms. Direct oxidation, which predominates when the exhaust-gas is fuel-lean, ispromoted by the adsorption of SOx species by the support. Under fuel-rich atmospheres, the presence of SO2 severelyinhibits steam reforming. The poisoning is associated with the formation of S2− on the platinum and of SO 4 2− on the support, but there is no indication of S-species being retained by the rhodium. It is proposed that each of the two mechanisms is sensitive to a different type of interaction at the metal-support interface. Direct oxidation is enhanced by the transfer of electrons from the precious metal to the support; steam reforming occurs at interfacial sites, which can be blocked by adsorbed SOx species.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00764084
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  • 70
    Digitale Medien
    Digitale Medien
    Oxidation of methanol at copper surfaces (1996)
    Springer
    Catalysis letters 37 (1996), S. 79-87 
    Details
    ISSN: 1572-879X
    Schlagwort(e): methanol ; oxidation ; copper ; electron spectroscopy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The role of preadsorbed oxygen present at Cu(111), Cu(110) and polycrystalline surfaces in the oxidation of methanol has been investigated by X-ray and electron energy loss spectroscopies. In addition to the well established formation of methoxy species and its subsequent decomposition and desorption as formaldehyde, a second reaction pathway to surface formate is present. The latter is temperature dependent being undetectable at 260 K at a polycrystalline surface but occurs at a significant rate at 295 K and above. The limitations of experimental data for methanol oxidation by temperature programmed desorption and molecular beam techniques are discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00813523
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  • 71
    Digitale Medien
    Digitale Medien
    Synergistic effects during CO oxidation over mixed oxides. Study of (Fe2O3+SnO2) and (Mn2O3+SnO2) systems (1996)
    Springer
    Catalysis letters 37 (1996), S. 181-185 
    Details
    ISSN: 1572-879X
    Schlagwort(e): synergistic effect ; carbon monoxide ; oxidation ; mixed oxides ; iron oxide ; tin oxide ; manganese oxide
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Based on the comparative evaluation of the catalytic activity of Fe2O3, Mn2O3 and SnO2 and their mixed oxides (Fe2O3+SnO2) and (Mn2O3+SnO2), it is shown that the system (Mn2O3+SnO2) shows strong synergistic effects during CO oxidation reaction. Such effects are not observed for the analogous system (Fe2O3+SnO2). Based on the calcination and reduction behaviour of these two mixed oxide systems and the redox potentials of the involved cations, the possible reasons for the observance of synergistic effects for the (Mn2O3+SnO2) system are discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00807751
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  • 72
    Digitale Medien
    Digitale Medien
    Non-uniform surface kinetics with two types of sites: the case of ethanol oxidation on molybdenum oxide (1996)
    Springer
    Catalysis letters 39 (1996), S. 67-71 
    Details
    ISSN: 1572-879X
    Schlagwort(e): non-uniform surface ; kinetics ; ethanol ; oxidation ; molybdenum oxide
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Temkin's theory of rates of catalytic reactions on non-uniform surfaces is extended to the MoO3-catalyzed oxidation of ethanol to acetaldehyde. Two types of sites are assumed to be present, an oxygen atom site that can be modeled with uniform properties and a metal atom site characterized by non-uniform properties both for ethanol chemisorption to an ethoxide intermediate and the conversion of this intermediate to acetaldehyde. The rate-limiting step is the cleavage of a C-H bond in the absorbed ethoxide intermediate. Non-uniform surface kinetics leads to a kinetic rate expression of the form $$v = kP_{C_2 H_5 OH}^{1 - m} P_{O_2 }^{(1 - m)/4} P_{H_2 O}^{ - (1 - m)/2} $$ . Such a rate expression, withm=0.14, is shown to provide a good fit to kinetic data for the selective oxidation of ethanol on a silica supported molybdenum oxide catalyst.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00813732
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  • 73
    Digitale Medien
    Digitale Medien
    Kinetics of the gas-solid heterogeneous photocatalytic oxidation of trichloroethylene by near UV illuminated titanium dioxide (1990)
    Springer
    Catalysis letters 4 (1990), S. 345-354 
    Details
    ISSN: 1572-879X
    Schlagwort(e): Ultraviolet heterogeneous photocatalysis ; oxidation ; trichloroethylene ; titania ; kinetics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Kinetics of the gas/solid heterogeneous photocatalytic oxidation of dilute trichloroethylene (TCE) vapors by ultraviolet-illuminated titanium dioxide have been determined using a fixed-bed dynamic photoreactor. Reaction rate dependences on inlet TCE, oxygen and water vapor concentrations were found to consist of both reactant sensitive and insensitive regions. In the reactant sensitive regions, measured limiting apparent reaction rate orders for TCE, oxygen and water vapor are 0.8, 1.7 and — 3, respectively. Water vapor in the reactant stream lowersinitial reaction rates relative to corresponding water free conditions, but is required to sustain photocatalytic activity for extended periods of time.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00765320
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  • 74
    Digitale Medien
    Digitale Medien
    Baeyer-Villiger rearrangement catalysed by titanium silicate molecular sieve (TS-1)/H2O2 system (1996)
    Springer
    Catalysis letters 40 (1996), S. 47-50 
    Details
    ISSN: 1572-879X
    Schlagwort(e): Baeyer-Villiger ; titanium silicate molecular sieve ; oxidation ; rearrangement ; titanium peroxo ; triphase
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Titanium silicate molecular sieve TS-1 has been found to be an efficient catalyst for Baeyer-Villiger (BV) oxidation of cyclic and aromatic ketones under triphase conditions (solid catalyst along with two immiscible liquid reactants in the absence of any cosolvent), using dilute H2O2. Reactions studied are the oxidation of cyclohexanone and acetophenone. Whereas in the case of cyclohexane,ε-caprolactone, a BV product along with hydroxy and diketones is formed, in the case of acetophenone, phenyl acetate, a BV product along witho- andp-hydroxyacetophenone is formed. The acidic nature of titanium peroxo species, stabilised by water, is proposed to be responsible for such reactions under triphasic reaction conditions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00807456
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  • 75
    Digitale Medien
    Digitale Medien
    Platinum particle size effect on the oxidative dehydrogenation of aqueous ethanol (1996)
    Springer
    Catalysis letters 36 (1996), S. 31-36 
    Details
    ISSN: 1572-879X
    Schlagwort(e): ethanol ; kinetics ; oxidation ; oxydehydrogenation ; platinum ; structure sensitivity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The effect of the platinum particle size was investigated for the catalytic oxidative dehydrogenation of aqueous ethanol to ethanal at a temperature of 303 K, an ethanol concentration of 260 mol m−3, a partial oxygen pressure 60 kPa, a pH of 9, and an ethanal and ethanoate concentration of 20 mol m−3. A particle size effect on the turnover frequency was observed but only for particle sizes smaller than 2 nm. Hence, the reaction shows a limited structure sensitivity.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00807202
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  • 76
    Digitale Medien
    Digitale Medien
    Perfluoroalkylporphyrin complexes as active catalysts for the reaction of isobutane with oxygen and the decomposition of tert-butyl hydroperoxide (1996)
    Springer
    Catalysis letters 36 (1996), S. 69-73 
    Details
    ISSN: 1572-879X
    Schlagwort(e): oxidation ; metalloporphyrins ; hydroperoxide decomposition
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract A new family of metalloporphyrin complexes having perfluoroalkyl groups in the meso-positions of the ring are active catalysts for the oxidation of isobutane to tert-butyl alcohol, TBA, and for the decomposition of tert-butyl hydroperoxide to TBA. This discovery extends the limited number of meso-substituents that can be used to enhance catalytic activity and fits the postulate that groups that withdraw electrons from the porphyrin periphery give rise to active catalysts for alkane oxidation. The perfluoroalkyl groups also confer oxidative stability, hydrophobicity and lower cost to the catalyst.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00807207
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  • 77
    Digitale Medien
    Digitale Medien
    The preparation and characterisation of nanometre platinum colloids on silicon wafers as model catalysts (1998)
    Springer
    Catalysis letters 50 (1998), S. 49-57 
    Details
    ISSN: 1572-879X
    Schlagwort(e): model catalysts ; spin coating ; Pt colloid ; AFM ; XPS ; Si wafer ; particle size ; oxidation ; reduction
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Platinum particles of 2 nm diameter have been immobilised on oxidised silicon wafers by spin coating with colloidal solutions and characterised by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The coverage and dispersion of the Pt colloids on the Si wafer are controlled by varying the concentration and the spin speed. Under optimal conditions mono-dispersed Pt colloids on silicon wafers are prepared. For the Pt colloids immobilised on the Si wafer, the majority of the stabilising ligands are removed through a reduction (with H2 at 200°C) or an oxidation (in air at 300°C) procedure. AFM showed that particle sizes are retained after the reduction procedure, while significant sintering occurs after oxidation. The mechanism of ligand removal was studied using an in situ XPS reaction cell.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1019062901616
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  • 78
    Digitale Medien
    Digitale Medien
    The CO2–CeO2 interaction and its role in the CeO2 reactivity (1998)
    Springer
    Catalysis letters 56 (1998), S. 199-202 
    Details
    ISSN: 1572-879X
    Schlagwort(e): cerium ; gas carbonic ; propane ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The interaction between CO2 and CeO2 and its role in the surface reactivity of alumina-supported cerium oxide has been studied by programmed thermodesorption (TPD) of CO2 and FTIR spectroscopy. The performance of Ce/Al2O3 systems was then analyzed for the propane oxidation in presence of CO2. The results have shown that the catalytic activity decreased when carbonate species are formed at the surface of CeO2. This behavior was attributed to the presence of CO2 from three different sources: contamination before use, during the handling of the samples, contamination proceeding from the reactants and from CO2 produced by the reaction itself.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1019098121432
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  • 79
    Digitale Medien
    Digitale Medien
    Effect of chloride on sintering of Pt/Al2O3 catalysts (1991)
    Springer
    Catalysis letters 8 (1991), S. 327-333 
    Details
    ISSN: 1572-879X
    Schlagwort(e): Platinum ; alumina ; oxichloride ; oxidation ; sintering
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Reduced Pt/Al2O3 catalysts with different chloride contents were treated at different temperatures under oxygen flow. TPR and TPD studies of oxidized species show that at low Cl/Pt atomic ratio (⩽1) PtO2 is formed at low temperature (400–500 K) and is totally decomposed (900 K) yielding reduced metallic Pt and inducing metal sintering. At high Cl/Pt atomic ratio (⩾6) formation of stable (up to 1000 K) platinum oxichloride avoids metal sintering.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00764194
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  • 80
    Digitale Medien
    Digitale Medien
    A new strategy for alkane oxidation with O2 using N‐hydroxyphthalimide (NHPI) as a radical catalyst (1999)
    Springer
    Catalysis surveys from Japan 3 (1999), S. 27-35 
    Details
    ISSN: 1572-8803
    Schlagwort(e): oxidation ; oxygen ; alkane ; N‐hydroxyphthalimide ; radical catalyst
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract A practical catalytic method to convert alkanes into the corresponding oxygen‐containing compounds with O2 under mild conditions using N‐hydroxyphthalimide (NHPI) in the presence or absence of a transition metal was developed. Thus, cyclohexane was successfully converted into adipic acid in good conversion and selectivity by a combined catalytic system consisting of NHPI and Mn(acac)2. Lower alkane such as isobutane was converted into t‐butyl alcohol (83%) under 10 atm of air by NHPI‐Co(OAc)2 system. Alkylbenzene such as toluene was oxidized to benzoic acid in high yield (81%) under normal temperature and pressure of dioxygen in the presence of a catalytic amount of NHPI and Co(OAc)2. ESR measurements showed that phthalimide‐N‐oxyl generated from NHPI under dioxygen atmosphere is a key species in this oxidation and functions as a radical catalyst.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1019059315516
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  • 81
    Digitale Medien
    Digitale Medien
    Bleaching of cellulose by hydrogen peroxide (1995)
    Springer
    Cellulose 2 (1995), S. 265-272 
    Details
    ISSN: 1572-882X
    Schlagwort(e): Hydrogen peroxide ; oxycellulose ; bleaching ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Abstract Peroxides are important bleaching agents, industrially, for cellulosic products. They are also used in detergents. Peroxides can degrade cellulose as well as decolorize it and remove stains. Both free radicals and perhydroxyl anions have been suggested as the intermediates in the reactions occurring between cellulosic products and hydrogen peroxide. The proposed mechanisms are reviewed with emphasis primarily on cotton cellulose. Further work is required to establish unequivocally the mechanism of degradation and decolorization of cellulose products.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00811817
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  • 82
    Digitale Medien
    Digitale Medien
    Effects of repeated manure and fertilizer phosphorus additions on soil phosphorus dynamics under a soybean-wheat rotation (1999)
    Springer
    Biology and fertility of soils 28 (1999), S. 150-155 
    Details
    ISSN: 1432-0789
    Schlagwort(e): Key words Phosphorus dynamics ; Olsen ; phosphorus ; Soil phosphorus fractions ; Manure ; Soybean-wheat rotation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract  Soil P availability and efficiency of applied P may be improved through an understanding of soil P dynamics in relation to management practices in a cropping system. Our objectives in this study were to evaluate changes in plant-available (Olsen) P and in different inorganic P (Pi) and organic P (P0) fractions in soil as related to repeated additions of manure and fertilizer P under a soybean-wheat rotation. A field experiment on a Typic Haplustert was conducted from 1992 to 1995 wherein the annual treatments included four rates of fertilizer P (0, 11, 22 and 44 kg ha–1 applied to both soybean and wheat) in the absence and presence of 16 t ha–1 of manure (applied to soybean only). With regular application of fertilizer P to each crop the level of Olsen P increased significantly and linearly through the years in both manured and unmanured plots. The mean P balance required to raise Olsen P by 1 mg kg–1 was 17.9 kg ha–1 of fertilizer P in unmanured plots and 5.6 kg ha–1 of manure plus fertilizer P in manured plots. The relative sizes of labile [NaHCO3-extractable Pi (NaHCO3-Pi) and NaHCO3-extractable P0 (NaHCO3-P0)], moderately labile [NaOH-extractable Pi (NaOH-Pi) and NaOH-extractable P0 (NaOH-P0)] and stable [HCl-extractable P (HCl-P) and H2SO4/H2O2-extractable P (resisual-P)] P pools were in a 1 : 2.9 : 7.6 ratio. Application of fertilizer P and manure significantly increased NaHCO3-Pi and -P0 and NaOH-Pi, and -P0 fractions and also total P. However, HCl-P and residual-P were not affected. The changes in NaHCO3-Pi, NaOH-Pi and NaOH-P0 fractions were significantly correlated with the apparent P balance and were thought to represent biologically dynamic soil P and act as major sources and sinks of plant-available P.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s003740050477
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  • 83
    Digitale Medien
    Digitale Medien
    Electrochemical oxidation of a carbon black loaded polymer electrode in aqueous electrolytes (1999)
    Springer
    Journal of solid state electrochemistry 3 (1999), S. 179-186 
    Details
    ISSN: 1433-0768
    Schlagwort(e): Key words Cathodic protection system ; Carbon ; oxidation ; Composite carbon/polymer anode ; Lifetime
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The suitability of a polymeric composite material for use as part of an anode structure in a cathodic protection system has been examined. The composite material was a conductive blend (volume resistivity typically 1.5 Ω cm) of carbon black in a polyethylene binder. A long operational lifetime for the material demands that the rate of carbon loss must be low. In the work reported here, electrochemical and in situ analytical techniques were employed to characterise the performance of the material over a wide range of anodic current densities in a variety of aqueous electrolytes. The predominant anodic electrochemical reaction on the polymeric material is CO2 formation in acid and neutral solutions, which causes loss of carbon from the surface and the development of a non-conducting layer of polyethylene. The characteristics of the reaction suggest that it occurs via the discharge of H2O. In alkaline pH, however, the anodic reactions are more complex. A high OH− concentration (pH 12 or higher) favours the formation of oxygen rather than CO2, particularly at low anodic potentials. The presence of CO3 2− in the electrolyte catalyses the evolution of oxygen at pH values as low as 9. The electrochemical formation of oxygen always occurs in parallel with the generation of some humic acid in the solution.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s100080050145
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  • 84
    Digitale Medien
    Digitale Medien
    Short-term dynamics in protein and amino acid metabolism (1997)
    Springer
    European journal of nutrition 36 (1997), S. 336-339 
    Details
    ISSN: 1436-6215
    Schlagwort(e): Amino acids ; protein ; metabolism ; meal feeding ; oxidation ; breath test ; Aminosäuren ; Protein ; Stoffwechsel ; Fütterung ; Oxidation ; Atemtest
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft , Medizin
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Die aktuellen Mengen an freien Aminosäuren im Blut reichen nur aus, um die Ganzkörper-Proteinsynthese für einige Minuten aufrecht zu erhalten. Das zeigt, daß die freien Aminosäurenkonzentrationen in der Zirkulation klein und konstant gehalten werden im Vergleich zu den Mengen der Aminosäuren, die täglich aufgenommen und über die Körperproteine umgesetzt werden. Das Verschwinden der Aminosäuren exogenen oder endogenen Ursprungs aus dem freien Aminosäuren-Pool, findet hauptsächlich durch die Proteinsynthese und den Aminosäurenabbau statt. Die Partitionierung der Nahrungs-Aminosäuren zwischen diesen beiden Prozessen im Kurzzeitbereich werden als bedeutsam für die Ökonomie der Ganzkörper-Aminosäuren angesehen. Eine Verbesserung der Aminosäurenökonomie könnte durch solche nutritiven Maßnahmen erreicht werden, welche die Clearance der Nahrungsaminosäuren durch die Proteinsynthese anstelle des Aminosäurenabbaus begünstigen. Diese nutritiven Maßnahmen sollten sich an den „Schwellenwerten“ des Abbaus der individuellen Aminosäuren orientieren.
    Notizen: Summary Actual amounts of free amino acids in the blood are sufficient to support whole body protein synthesis for some minutes only. This indicates that the levels of free amino acids in the circulation are kept small and constant relative to the amounts of amino acids supplied by daily intake and turnover of body proteins. The clearance of the amino acids originating from either endogenous or exogenous sources is mainly due to protein synthesis and metabolic degradation. The partitioning of dietary amino acids between these processes, on the short term, is supposed to play an important role in whole body amino acid economy. Therefore whole body amino acid economy could be improved by nutritional measures that favour the clearance of dietary amino acids by protein synthesis instead of by metabolic degradation. These nutritional measures should to be focused on threshold values for metabolic degradation of individual amino acids.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01617818
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  • 85
    Digitale Medien
    Digitale Medien
    Determination of P/Al ratio in phosphorus-doped aluminium oxide thin films by XRF, RBS and FTIR (1995)
    Springer
    Microchimica acta 119 (1995), S. 13-22 
    Details
    ISSN: 1436-5073
    Schlagwort(e): aluminium oxide ; phosphorus ; XRF ; RBS ; FTIR
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Phosphorus-doped aluminium oxide thin films were deposited in a flow-type ALE reactor from AlCl3, H2O and from either P2O5 or trimethyl-phosphate. Structural information of the films was obtained from Fourier transform infrared (FTIR) spectra. Rutherford backscattering spectroscopy (RBS) was used to quantitatively determine the composition of the films. The P/Al intensity ratios calculated from X-ray fluorescence (XRF) results were in a linear relation with the P/Al concentration ratios calculated from RBS results. For comparison, the intensity ratios of the phosphorus peak (P=O) at about 1250 cm−1 and the aluminium peak (Al-O) at about 950 cm−1 were determined from the IR absorption spectra. The calibration of FTIR peak intensities was done by plotting the intensity ratios of phosphorus and aluminium peaks against the P/Al concentration ratios measured by RBS. FTIR gave also a linear calibration curve with RBS but the method is less suitable for routine analysis of P/Al ratio than XRF.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01244850
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  • 86
    Digitale Medien
    Digitale Medien
    Manganese(III) oxidations of benzoylhydrazine, aroxyacetylhydrazine, semicarbazide, thiosemicarbazide and their derivatives in pyrophosphate media (1994)
    Springer
    Microchimica acta 113 (1994), S. 61-69 
    Details
    ISSN: 1436-5073
    Schlagwort(e): manganese(III) ; pyrophosphate ; oxidation ; hydrazines ; hydrazides ; carbazides ; potentiometry
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Manganese(III) ion was stabilised in weakly acidic solution by means of pyrophosphate. Conditions for the quantitative oxidation of hydrazine, benzoylhydrazines, aroxyacetylhydrazines, semicarbazide, semicarbazones, thiosemicarbazide and thiosemicarbazones were investigated by titrimetric and potentiometric methods. The stoichiometries of these oxidations were pH-dependent. At pH 5 benzoyl hydrazines were oxidised by donating two electron each, the nitro derivative being the sole exception to show a three-electron change. Aroxyacetylhydrazines, semicarbazide and semicarbazones underwent three-electron oxidations. The free radical nature of these reactions was illustrated. Thiosemicarbazides reacted faster than semicarbazides. Metal complexes of thiosemicarbazide also yielded stoichiometric results, indicative of the number of TSC ligands in the complex. The oxidation products have been identified. At pH ⩽ 1 these reactions conformed to different stoichiometries.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01243138
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  • 87
    Digitale Medien
    Digitale Medien
    Estimation of mercaptans with 1-chlorobenzotriazole (1990)
    Springer
    Microchimica acta 102 (1990), S. 271-276 
    Details
    ISSN: 1436-5073
    Schlagwort(e): mercaptans ; oxidation ; disulphide ; Chlorobenzotriazole ; potentiometry
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract A simple but accurate potentiometric method for the estimations of mercaptans in 0.01M perchloric acid has been developed, based on their oxidation with 1-Chlorobenzotriazole. Quantitative oxidation solely to the disulphide stage is ensured by using critical amounts of methanol, acetonitrile and potassium iodide. Chloride, mercury(II) and copper(II) interfere. A back-titration procedure can also be used. The oxidation products have been identified.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01244768
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  • 88
    Digitale Medien
    Digitale Medien
    Determination of phosphorus, sulfur and chlorine in high-purity aluminium (1990)
    Springer
    Microchimica acta 101 (1990), S. 273-279 
    Details
    ISSN: 1436-5073
    Schlagwort(e): aluminium analysis ; phosphorus ; sulfur ; chlorine
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Multi-step procedures for the determination of phosphorus, sulfur and chlorine are described and tested against established methods and on reference materials. Phosphorus is separated as hydrogen phosphide, extracted as phosphomolybdic acid, reduced to molydenum blue and measured photometrically (detection limit 0.05 μg/g). Sulfur is separated after reduction as hydrogen sulfide or by means of pyrohydrolysis and measured by ICP-OES (detection limit 0.1 μg/g). Chloride can be measured by ion chromatography after pyrohydrolytic separation (detection limit 0.1 μg/g). The determination of sulfur was also successfully tested on copper and steel samples.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01244179
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  • 89
    Digitale Medien
    Digitale Medien
    The determination of phosphonate base scale inhibitors in brines by plasma spectrometry (1992)
    Springer
    Microchimica acta 109 (1992), S. 201-209 
    Details
    ISSN: 1436-5073
    Schlagwort(e): phosphonate base scale inhibitor ; brine ; direct current plasma ; inductively coupled plasma atomic emission spectrometry ; phosphorus
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The determination of phosphonate base scale inhibitors in brines by direct current plasma (DCP) and inductively coupled plasma atomic emission spectrometry (ICP-AES) is described. The first method is based on a direct nebulization of the brine samples and plasma using the phosphorus line at 213.618 nm. The second method involves extraction of phosphorus as phospho-antimonyl molybdate complex into methylisobutyl ketone (MIBK) phase and analysis of the extract for molybdenum using the Mo 313.260 nm line. Comparison between the proposed methods and an established recommended method [1] shows excellent agreement between the results in addition to the sensitivity and ease of automation provided by AES.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01242475
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  • 90
    Digitale Medien
    Digitale Medien
    The oxidation behaviour of niobium containing γ-TiAl based intermetallics in air and argon/oxygen (1995)
    Springer
    Microchimica acta 119 (1995), S. 23-39 
    Details
    ISSN: 1436-5073
    Schlagwort(e): oxidation ; titanium aluminide ; SNMS ; niobium effect ; oxygen tracer
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The oxidation behaviour of γ-TiAl based alloys with different Nb contents (2–10 At.%) was investigated in air and in argon-20% oxygen at 900 °C using thermogravimetric analysis. The oxide scales were characterized by a combination of optical microscopy, SEM/EDX and X-ray diffraction analyses. Although in all studied cases the presence of niobium improves the oxidation resistance of γ-TiAl, the oxidation kinetics, scale morphology and composition in air differed strongly from that in argon-oxygen. In air the oxidation resistance increases with increasing niobium-content. In Ar/O2 the niobium dependence is far more complex because internal oxidation occurs which is favoured by the presence of niobium. SNMS analysis revealed that the differences in behaviour in the two atmospheres are related to the formation of Ti-rich nitride at the scale/alloy interface during air oxidation. The positive effect of niobium on the oxidation resistance of γ-TiAl is mainly caused by a decrease of the transport processes in the heterogeneous TiO2/Al2O3-surface scale. Nitride formation and/or niobium enrichment at the scale/alloy interface also affect the oxidation behaviour, however these factors are believed to be the result of the decreased transport processes rather than the main reason for the niobium effect.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01244851
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  • 91
    Digitale Medien
    Digitale Medien
    C60: A host lattice for the intercalation of oxygen? (1997)
    Springer
    Microchimica acta 125 (1997), S. 401-406 
    Details
    ISSN: 1436-5073
    Schlagwort(e): fullerenes ; intercalation ; oxidation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The investigation of structural and electronic properties of the novel family of fullerenes depends on the existence of pure reference materials. Sublimation of the van-der Waals solids is a suitable purification method. Little attention has been paid to the question about the air stability of such sublimed samples in form of crystals or thin films. A combination of thermal desorption spectroscopy, thermal analysis and diffuse reflectance FT-IR spectroscopy is used to show the extent to which oxygen from dry air is intercalated into fullerenes and which detrimental reactivity occurs from attempts to thermally remove („nneal”) air-exposed samples. The conclusion is that any fullerene sample exposed to air will be transformed in part into a polymeric non-fullerene carbon upon thermal treatment to above 400 K irrespective of its initial purity.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01246218
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  • 92
    Digitale Medien
    Digitale Medien
    Historical changes in sediments of Pyramid Lake, Nevada, USA: consequences of changes in the water balance of a terminal desert lake (1994)
    Springer
    Journal of paleolimnology 12 (1994), S. 87-101 
    Details
    ISSN: 1573-0417
    Schlagwort(e): Great Basin ; climatic variations ; productivity ; organic matter ; nitrogen ; phosphorus ; hardwater lake
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Geologie und Paläontologie
    Notizen: Abstract Sediment cores from the shallow and deep basins of Pyramid Lake, Nevada, revealed variations in composition with depth reflecting changes in lake level, river inflow, and lake productivity. Recent sediments from the period of historical record indicate: (1) CaCO3 and organic content of sediment in the shallow basin decrease at lower lake level, (2) CaCO3 content of deep basin sediments increases when lake level decreases rapidly, and (3) the inorganic P content of sediments increases with decreasing lake volume. Variations in sediment composition also indicate several periods for which productivity in Pyramid Lake may have been elevated over the past 1000 years. Our data provide strong evidence for increased productivity during the first half of the 20th Century, although the typical pattern for cultural eutrophication was not observed. The organic content of sediments also suggests periods of increased productivity in the lake prior to the discovery and development of the region by white settlers. Indeed, a broad peak in organic fractions during the 1800's originates as an increase starting around 1600. However, periods of changing organic content of sediments also correspond to periods when inflow to the lake was probably at extremes (e.g. drought or flood) indicating that fluctuations in river inflow may be an important factor affecting sediment composition in Pyramid Lake.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00678089
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  • 93
    Digitale Medien
    Digitale Medien
    An expanded weighted-averaging model for inferring past total phosphorus concentrations from diatom assemblages in eutrophic British Columbia (Canada) lakes (1995)
    Springer
    Journal of paleolimnology 14 (1995), S. 49-67 
    Details
    ISSN: 1573-0417
    Schlagwort(e): diatoms ; eutrophication ; lake management ; paleolimnology ; British Columbia ; lakes ; phosphorus ; training sets
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Geologie und Paläontologie
    Notizen: Abstract Eighteen lakes were added to a published training set of 46 British Columbia (BC) lakes in order to expand the original range of total phosphorus (TP) concentrations. Canonical correspondence analysis (CCA) was used to analyze the relationship between diatom assemblages and environmental variables. Specific conductivity and [TP] each explained significant (P≤0.05) directions of variance in the distribution of the diatoms. The relationship between diatom assemblages and [TP] was sufficiently strong to warrant the development of a weighted-averaging (WA) regression and calibration model that can be used to infer past trophic status from fossil diatom assemblages. The relationship between observed and inferred [TP] was not improved by the addition of more eutrophic lakes, however the [TP] range and the number of taxa used in the transfer function are now superior to the original model. Diatom species assemblages changed very little in lakes with TP concentrations greater than 85 µg 1−1, so we document the development of a model containing lakes with TP≤85 µg 1−1. The updated model uses 59 training lakes and covers a range of species optima from 6 to 41.9 µg 1−1 TP, and a total of 150 diatom taxa. The updated inference model provided a more realistic reconstruction of the anthropogenic history of a highly eutrophic BC lake. The model can now be used to infer past nutrient conditions in other BC lakes in order to assess changes in trophic status.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00682593
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  • 94
    Digitale Medien
    Digitale Medien
    Variability of diatom-inferred phosphorus profiles in a small lake basin and its implications for histories of lake eutrophication (1998)
    Springer
    Journal of paleolimnology 20 (1998), S. 47-55 
    Details
    ISSN: 1573-0417
    Schlagwort(e): diatoms ; spatial variability ; canonical correspondence analysis ; lake eutrophication ; transfer functions ; phosphorus
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Geologie und Paläontologie
    Notizen: Abstract Diatom analyses were undertaken of sediment cores covering a range of water depths in a small eutrophic lake (Lough Augher, Co. Tyrone, N. Ireland). The significance of between-core variability in diatom relative frequency stratigraphy was assessed by Canonical Correspondence Analysis (CCA) where the ordination axes were constrained to external environmental variables (sediment depth, core location coordinates, water depth, effective fetch, distance-from-shore and distance-from-inflow). After the removal of the effect of sediment age by partialling it out, the resultant first two axes from the partial-CCA were significantly correlated with water depth and distance-from-shore, indicating non-uniform diatom stratigraphies across the lake. Despite this variability, all cores show the same succession of species and, therefore, record the eutrophication of the lake. Diatom-inferred total phosphorus (DI-TP) was inferred for six cores using weighted averaging regression and calibration. Apart from considerable differences of DI-TP in surficial sediment samples, there was good between-core repeatability of DI-TP profiles. These data support the use of DI-TP for establishing background nutrient concentrations for lakes, and associated implications for lake restoration schemes using single cores. Comparisons of DI-TP profiles and total diatom accumulation rate data for the individual cores indicate that diatom production peaked prior to the maximum TP concentrations in the lake.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1007923813511
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  • 95
    Digitale Medien
    Digitale Medien
    Stable isotope (δ13C and δ15N) signatures of sedimented organic matter as indicators of historic lake trophic state (1999)
    Springer
    Journal of paleolimnology 22 (1999), S. 205-221 
    Details
    ISSN: 1573-0417
    Schlagwort(e): carbon isotopes ; diatoms ; lake management ; nitrogen isotopes ; phosphorus ; radium-226 ; sediments ; trophic state
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Geologie und Paläontologie
    Notizen: Abstract We explored the use of carbon and nitrogen isotopes (δ13C and δ15N) in sedimented organic matter (OM) as proxy indicators of trophic state change in Florida lakes. Stable isotope data from four 210Pb-dated sediment cores were compared stratigraphically with established proxies for historical trophic state (diatom-inferred limnetic total phosphorus, sediment C/N ratio) and indicators of cultural disturbance (sediment total P and 226Ra activity). Diatom-based limnetic total P inferences indicate a transition from oligo-mesotrophy to meso-eutrophy in Clear Lake, and from eutrophy to hypereutrophy in Lakes Parker, Hollingsworth and Griffin. In cores from all four lakes, the carbon isotopic signature of accumulated OM generally tracks trophic state inferences and cultural impact assessments based on other variables. Oldest sediments in the records yield lower diatom-inferred total limnetic P concentrations and display relatively low δ13C values. In the Clear, Hollingsworth and Parker records, diatom-inferred nutrient concentrations increase after ca. AD 1900, and are associated stratigraphically with higher δ13C values in sediment OM. In the Lake Griffin core, both proxies display slight increases before ~1900, but highest values occur over the last ~100 years. As Lakes Clear, Hollingsworth and Parker became increasingly nutrient-enriched over the past century, the δ15N of sedimented organic matter decreased. This reflects, in part, the increasing relative contribution of nitrogen-fixing cyanobacteria to sedimented organic matter as primary productivity increased in these waterbodies. The Lake Griffin core displays a narrow range of both δ13C and δ15N values. Despite the complexity of carbon and nitrogen cycles in lakes, stratigraphic agreement between diatom-inferred changes in limnetic total P and the stable isotope signatures of sedimented OM suggests that δ13C and δ15N reflect shifts in historic lake trophic state.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008078222806
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  • 96
    Digitale Medien
    Digitale Medien
    Calibration of diatoms along a nutrient gradient in Florida Everglades Water Conservation Area-2A, USA (1999)
    Springer
    Journal of paleolimnology 22 (1999), S. 413-437 
    Details
    ISSN: 1573-0417
    Schlagwort(e): diatoms ; Everglades ; phosphorus ; wetland ; calibration ; multivariate ; Florida
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Geologie und Paläontologie
    Notizen: Abstract The relationship between diatom taxa preserved in surface soils and environmental variables at 31 sites in Water Conservation Area 2A (WCA-2A) of the Florida Everglades was explored using multivariate analyses. Surface soils were collected along a phosphorus (P) gradient and analyzed for diatoms, total P, % nitrogen (N), %carbon (C), calcium (Ca), and biogenic silica (BSi). Phosphorus varied from 315-1781 μg g-1, and was not found to be correlated with the other geochemical variables. Canonical correspondence analysis (CCA) was used to examine which environmental variables correlated most closely with the distributions in diatom taxa. Canonical correspondence analysis with forward selection, constrained and partial CCA, and Monte Carlo permutation tests of significance show the most significant changes in diatom assemblages along the P gradient (p 〈 0.01), with additional species differences correlated with soil C, N, Ca, and BSi. Weighted-averaging (WA) regression and calibration models of diatom assemblages to P and BSi were developed. The diatom-based inference model for soil [P] had a high apparent r2 (0.86) with RMSEboot = 218 μg g-1. Indicator diatom species identified by assessing species WA optima and WA tolerance to [P], such as Nitzschia amphibia and N. palea for high [P] (~1300-1400 μ g-1) and Achnanthes minutissima var. scotica and Mastogloia smithii for low [P] (~400-600 μg g-1), may be useful as monitoring tools for eutrophication in WCA-2A as well as other areas of the Everglades. Diatom assemblages analyzed by cluster analysis were related to location within WCA-2A, and dominant taxa within clusters are discussed in relation to the geochemical variables measured as well as hydrology and pH. Diversity of diatom assemblages and a ‘Disturbance Index’ based on diatom data are discussed in relation to the historically P-limited Everglades ecosystem. Diatom assemblages should be very useful for reconstructions of [P] through time in the Florida Everglades, provided diatoms are well preserved in soil cores.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008049224045
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  • 97
    Digitale Medien
    Digitale Medien
    Modern and historic accumulation rates of phosphorus in Lake Okeechobee, Florida (1998)
    Springer
    Journal of paleolimnology 20 (1998), S. 31-46 
    Details
    ISSN: 1573-0417
    Schlagwort(e): phosphorus ; Lake Okeechobee ; lead-210 dating ; eutrophication ; phosphorus loading
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Geologie und Paläontologie
    Notizen: Abstract Phosphorus accumulation rates in depositional zone sediments of Lake Okeechobee were determined in 11 mud-zone cores and two peat-zone cores dated by 210Pb. Although difficulties were encountered in interpreting 210Pb data from some sites, reliable dating of sediments from the mud zone of this shallow lake is possible. Sediment accumulation rates in this zone have increased during the present century by an average of about twofold, and accumulation of organic sediments in the lake during pre-settlement times apparently was much slower than during the past century. Concentrations of all forms of sedimentary P but especially nonapatite inorganic-P and organic-P also have increased since pre-settlement times and especially since about 1940. Annual P accumulation rates in the lake's sediments have increased about fourfold during the 1900s, with most of the increase occurring in the past 40–50 years. The recent accumulation rate of sedimentary P (past ~ 10 years) agrees within a factor of 1.5 with the net retention of P in the lake calculated from published input-output mass balances.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1007939714301
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  • 98
    Digitale Medien
    Digitale Medien
    Factors affecting the oxidation of elemental sulfur in soils (1993)
    Springer
    Nutrient cycling in agroecosystems 35 (1993), S. 101-114 
    Details
    ISSN: 1573-0867
    Schlagwort(e): Elemental sulfur ; oxidation ; S fertilizers ; thiobacilli ; heterotrophic S-oxidizers
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract The use of elemental sulfur (S0) to alleviate widespread S deficiencies in agricultural soils is limited by the unpredictability of its oxidation to plant available sulfate. Here we review the biological, fertilizer and soil-related factors that control S0 oxidation. Sulfur oxidation in soil is mediated primarily by microorganisms, and thus it is the size, composition and activity of the microbial community which dictate oxidation rates. Because S0 oxidation is a biological process, it is strongly influenced by factors directly affecting microbial activity including soil temperature, water potential, and aeration. In many soils these factors represent the primary constraints to S0 oxidation. Oxidation is also influenced by the effective surface area of the S exposed to microbial activity. Thus oxidation is favored by reducing the particle size and abundant populations of heterotrophic bacteria and fungi capable of oxidizing S0, thus the availability of organic substrates from residue additions or root exudates may also affect S oxidation. Previous application of S0 may increase oxidation rates in many soils, presumably by stimulating S0 oxidizing populations. The large number of factors that govern S0 oxidation account for the variability in oxidation rates among soils, climatic regions, and agronomic practices. Many of these factors are subject to agronomic control, however, and it should be possible to devise S fertilizer strategies that exploit the slow release characteristics of S0 to meet crop demands efficiently in a variety of conditions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00750224
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  • 99
    Digitale Medien
    Digitale Medien
    Hydrology of the Peel-Harvey estuary catchment (1993)
    Springer
    Nutrient cycling in agroecosystems 36 (1993), S. 127-133 
    Details
    ISSN: 1573-0867
    Schlagwort(e): hydrology ; water balance ; phosphorus ; Streamflow ; Peel-Harvey
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract This paper discusses the land types, hydrologic characteristics and processes, and the major modification of these, in relation to mechanisms and magnitude of phosphorus losses to drains and riverine systems which discharge to the Peel-Harvey estuary. About 75% of the coastal plain part of the catchment is cleared of native vegetation and used for dryland, dairy and beef grazing. There are small areas devoted to irrigated pasture and commercial horticulture. Seventy-five percent of the soils of the catchment are sandy surfaced with a poor capacity to retain phosphorus. Though the area is flat, catchment water yields are high because of a large winter rainfall excess and low soil storage capacity. Drainage schemes have been constructed in much of the catchment to remove excess water quickly. This was required initially to allow agricultural expansion and is now important for protecting a growing infrastructure which serves the most populous region of Western Australia.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00747583
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  • 100
    Digitale Medien
    Digitale Medien
    Environmental impact of fertilizing soils by using sewage and animal wastes (1994)
    Springer
    Nutrient cycling in agroecosystems 37 (1994), S. 1-22 
    Details
    ISSN: 1573-0867
    Schlagwort(e): animal slurries and manures ; applications to soils ; carbon- ; nitrogen- ; phosphorus ; contamination ; crop production ; dissemination ; hazardous organics ; heavy metals ; inputs ; macro- and micronutrients ; pathogens ; sewage sludges ; survival- ; transfer- ; transport and adsorption rates in soils
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract The European Community is producing annually about 300 × 106 tons of sewage sludges as well as about 150, 950,160 and 200 tons of domestic, agricultural, industrial and other wastes (street litter, dead leaves etc.). About 20–25% of the German sewage sludges, which contain in average about 3.8,1.6, 0.4, 0.6, 5.3% DM−1 N, P, K, Mg and Ca, 202, 5, 131, 349, 53, 3 and 1446 mg kg−1 DM Pb, Cd, Cr, Cu, Ni, Hg, Zn as well as ca. 37 and 5 mg kg−1 Dm polychlorinated hydrocarbons and biphenyls, are recycled annually as fertilizer. In addition environmental impacts on the arable land of Germany may derive from 76,19.2, 64.7, 33.6, 7.8 and 0.1 kg ha−1 a−1 of N, P, K, Ca, Mg and Cu added as animal manures. Besides heavy metals and hazardous organics pathogens are disseminated with organic wastes. Crop production and soil fertility generally profit from the considerable amounts of plant nutrients and carbon in sewage sludges, animal slurries and manures, but the physicochemical soil properties, the composition of microbial, faunal and plant communities as well as the metabolic processes in the soil-, rhizo- and phyllosphere are changed by organic manuring. Consequences for the soil carbon-, nitrogen-and phosphorus-cycle are discussed. Impacts of heavy metals and hazardous organics on the soil biomass and its habitat as well as on transport mechanisms and surival times of disseminated pathogens in soils are reviewed with emphasis on the German situation. A proposal for future strategies (landscape recycling) is made.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00750669
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