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  • Springer  (6)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Catalysis letters 43 (1997), S. 219-228 
    ISSN: 1572-879X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The evolution of the acid/base properties of a series of oxide supports (alumina, magnesia and silica) modified by increasing loadings of additive ions (Li+, Ni2+, and SO4 2-) from 1 to 50% of the support surface coverage is reported using the catalytic test of isopropanol decomposition, studied as a function of the reaction temperature. The calculated kinetic parameters Ea, A, and ΔS≠ permit interpretation of the reaction mechanism with relation to the acidity/basicity of the modified surfaces. The series of alumina oxides, due to the amphoteric properties of the surfaces, decomposed isopropanol through an E2 mechanism leading to propene and di-isopropyl ether formation. The selectivity to the two products was dependent on the strength of the basicity (addition of lithium and nickel) or on the acidity (addition of sulfate) of the surfaces. Magnesia series oxides dehydrated isopropanol through an E1b mechanism due to the presence of very strong basic surfaces possessing some weak acid sites. The very weak amphoteric character of silica was strengthened by the loading of the three additives; the modified silica surfaces displayed enhanced decomposition activity with respect to pure silica.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Catalysis letters 48 (1997), S. 39-46 
    ISSN: 1572-879X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A study of the activity and durability of two different copper chromite catalysts in methane combustion is presented. The catalysts, a massive (CAT-E) and a supported (CAT-I) copper chromite, were characterized by different techniques in order to investigate morphological properties (N2 adsorption), crystalline structure (X-ray diffraction, XRD) and surface composition (X-ray photoelectron spectroscopy, XPS). Among the different crystalline phases identified, CuCr2O4 spinel represented the common phase in both the catalysts. The CrVI/CrIII surface ratio was almost the same for the two catalysts, while the CuII/CuI surface ratio was much higher on the massive catalyst than on the supported one. The activity for CH4 combustion was studied in the temperature range 300-700°C at constant CH4:air ratio of 1:30 and constant methane content, 1.2%. The activity was higher for CAT-I and CAT-E showed better stability. A kinetic study from the catalytic data, collected at different contact times in the interval 0.047-0.315 s as a function of temperature, provided a value of about 110 kJ/mol for the activation energy. This value was obtained for various degrees of methane converted for the two catalysts. The reaction rates were between 10-3 and 10-4 (molCH4)conv/(g h) in the temperature interval 550-700°C, for both the catalysts.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of thermal analysis and calorimetry 37 (1991), S. 1737-1744 
    ISSN: 1572-8943
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die AziditÄt und BasizitÄt von rund zwanzig vorwiegend in der Katalyse verwendeten einfachen Metalloxiden und keramischen Materialien wurden durch Adsorptions-Mikrokalorimetrie mittels basischer und saurer gasförmiger Probenmoleküle, wie Ammoniak and Kohlendioxid, bestimmt. Aus der Ermittlung der Anzahl, StÄrke und Energieverteilung sowohl saurer als auch basischer Adsorptionstellen in sÄmtlichen Proben ergab sich eine verbesserte Beschreibung deren OberflÄchen. Die Resultate erlaubten die Einteilung der untersuchten Proben in drei auf ihren sauren, basischen oder amphoteren Charakter bezogene Hauptgruppen. Das SÄure-Base-Verhalten wurde versuchsweise korreliert mit allgemeineren, aus der Literatur zugÄnglichen Daten bezüglich elektronischer Eigenschaften und Redoxverhalten, wie beispielsweise die ElektronegativitÄt.
    Notes: Abstract The acidity and basicity of about twenty simple oxides mainly used in catalysis and ceramic materials were investigated by adsorption microcalorimetry of basic and acidic gas probe molecules such as ammonia and carbon dioxide. The determination of the number, strength and site energy distribution of both acidic and basic sites in all the samples led to an improved description of the surfaces. The results allowed us to classify our samples in three main groups in relation to their acidic, basic or amphoteric character. Their acid-base behaviour was tentatively correlated to more general electronic and redox data given in the literature such as the electronegativity.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Journal of thermal analysis and calorimetry 56 (1999), S. 1233-1241 
    ISSN: 1572-8943
    Keywords: adsorption microcalorimetry ; Ga2O3 ; NH3 ; NO2 ; SnO2 ; SO2
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The surface properties of gallium oxide and tin dioxide supported on alumina or titania have been studied by adsorption microcalorimetry. The differential heats of adsorption of various pollutant adsorbates such as sulfur dioxide, nitrogen monoxide, nitrogen dioxide and also ammonia were measured on these catalytic surfaces. NH3, SO2, NO2 are strongly adsorbed while NO is only physisorbed. The supported Ga2O3 samples show a slight decrease in acidity as probed by ammonia adsorption, compared to alumina or titania. The addition of SnO2 decreases the number of strong acid sites but creates a few weak and medium strength acid sites on alumina and does not modify the acidity of titania. In all cases, the basicity, probed by SO2 adsorption, is very strongly affected by the deposition of Ga2O3 or SnO2. The differential heats of NO2 adsorption remain nearly constant on all samples. The heats of adsorption are discussed as a function of the coverage and of the amount of guest oxide.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Reaction kinetics and catalysis letters 68 (1999), S. 229-235 
    ISSN: 1588-2837
    Keywords: Oxide catalysts ; acid-base properties ; COS formation ; initial activity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Among various acidic, basic and amphoteric oxides La2O3 and ThO2, both having strong ionic character and peculiar acid-base properties, exhibited outstanding initial catalytic activity in the CO2+CS2=2COS reaction.
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  • 6
    Publication Date: 2020-05-08
    Print ISSN: 0022-2461
    Electronic ISSN: 1573-4803
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Springer
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