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  • 1
    Electronic Resource
    Electronic Resource
    Mechanism of but-1-ene hydrogenation and isomerization on oxygen-modified bulk tungsten carbides using deuterium tracer studies. Effect of oxygen treatment on hydrogen dissociation (1997)
    Springer
    Catalysis letters 47 (1997), S. 63-69 
    Details
    ISSN: 1572-879X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The catalytic behaviours of bulk tungsten carbides differently modified by air treatments have been studied in hydrogenation (or deuteration) and double-bond isomerization of but-1-ene, in hydrogen/deuterium exchange of methylcyclopentane, as well as in hydrogen dissociation via H2/D2 exchange. Two kinds of catalyst samples have been studied. The first sample has been treated by air at moderate temperature (350°C) and the second at high temperature (700°C). It was found that, for but-1-ene reaction at temperatures varying between 30 and 100°C, but-2-enes are the main products formed, and only a small amount of hydrogenated products was detected for both catalysts. Two possible double-bond migration mechanisms by an intramolecular hydrogen migration, either with π-olefinic, π-allylic and metallacyclobutane or with π-olefinic and π-allylic species interconversions are deduced; these mechanisms occur without the participation of dissociated hydrogen or deuterium atoms. However, it has been demonstrated that the hydrogen dissociation temperature is a function of the air treatment of the bulk tungsten carbide, even if this property has no effect on the hydrogenation of but-1-ene to n-butane. Thus, in order to see the influence of oxygen modification, a more detailed study has been carried out. Starting from a bulk tungsten carbide without oxygen, several controlled oxygen additions have been made, leading to four different samples. The HD formation has been analyzed for each sample as a function of temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019063828565
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  • 2
    Electronic Resource
    Electronic Resource
    Catalytic activity and XPS surface determination of tungsten carbide for hydrocarbon reforming. Influence of the oxygen (1995)
    Springer
    Catalysis letters 35 (1995), S. 65-74 
    Details
    ISSN: 1572-879X
    Keywords: tungsten carbide ; oxygen ; alkane reforming
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The influence of oxygen on the catalytic properties of tungsten carbide has been studied for the reforming reaction of 2-methylpentane in a great excess of hydrogen $$\left( {P_{H_2 } /P_{HC} = 150} \right)$$ . The oxygen surface concentration has been measured by the ratio of the signal area of the O1s and the W4f levels as determined by X-ray photoelectron spectroscopy. Two kinds of processes are observed: cracking and isomerization reactions. The introduction of oxygen at T=350°C leads to a deep decrease of the cracking reaction kinetics; about two orders of magnitude. The tungsten carbide, strongly selective for cracking reactions in absence of oxygen, becomes very selective for isomer production in the presence of oxygen.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00807005
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  • 3
    Electronic Resource
    Electronic Resource
    Surface characterization and catalytic properties of supported tungsten and platinum-tungsten carbide and oxycarbide (1994)
    Springer
    Topics in catalysis 1 (1994), S. 75-85 
    Details
    ISSN: 1572-9028
    Keywords: Bulk and supported tungsten carbides ; oxycarbides ; supported platinumtungsten carbides ; tungsten aluminate ; XPS ; argon ion bombardment ; skeletal rearrangement of hydrocarbons
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Bulk tungsten carbide has been prepared from ammonium paratungstate. Oxidic oxygen in relatively small amount is always present on the WC surface regardless of the method of carburization. Tungsten(VI) oxide in Al2(WO4)3 can be reduced directly and in apparently one single step to the elemental W(0) state by Ar+ bombardment. Under H2 the reduction starts at 720 K. In 12 and 28% W03 supported on γ-Al2O3 and in Al2(WO4)3, almost 90% of the tungsten could be converted to the carbide form. Extensive hydrogenolysis products for n-hexane reactions on freshly prepared WC were observed while selectivity to isomerization associated with decrease in activity occurs upon exposure of the WC to oxygen at 620 K. Supported tungsten carbide(s) and oxycarbide(s) on γ-Al2O3 have comparable catalytic behaviour to those obtained on the bulk systems. The presence of Pt in these supported systems did not improve the catalytic performances and even did not show the catalytic properties of Pt. This was attributed to the severe conditions of catalyst preparations. Although the catalytic activity of tungsten carbide(s) obtained from the carburization of Al2(WO4)3 is very low, the selectivity suggests the presence of tungsten carbide plus some WO, species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01379577
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  • 4
    Electronic Resource
    Electronic Resource
    Tungsten carbides as substitutes of platinoids in heterogeneous catalysis I. The effect of surface composition on the reactivity of methylcyclopentane on tungsten carbides (1991)
    Springer
    Catalysis letters 10 (1991), S. 137-148 
    Details
    ISSN: 1572-879X
    Keywords: Methylcyclopentane reactivity ; tungsten carbides ; heterogeneous catalysis ; surface composition ; hydrogenolysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Reactions of methylcyclopentane on tungsten carbides show that in presence of oxygen the extensive hydrogenolysis is inhibited in favour of ring enlargement and ring opening via a bifunctional mechanism due to the coexistence of surface acid-rearrangement and hydrogenation-dehydrogenation sites. The oxycarbidic materials are very active and selective in skeletal rearrangement of hydrocarbons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00772066
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  • 5
    Electronic Resource
    Electronic Resource
    The multi-structure of oxidized-reduced tungsten carbide surface(s) (1994)
    Springer
    Catalysis letters 29 (1994), S. 397-408 
    Details
    ISSN: 1572-879X
    Keywords: tungsten carbide ; surface composition ; XPS ; argon ion bombardment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The XPS of bulk tungsten carbide, partially oxidized WC surfaces at 373 and 573 K as well as tungsten trioxide have been reported. Bulk WC has been prepared from WO3 as a starting material in a mixture of CH4 (20%) and H2 (80%) at 1150 K for 4 h, while partially oxidized WC surfaces were prepared by oxygen chemisorption on a clean WC surface at 200 K, then the temperatures were raised to 373 and 573 K respectively. The XPS of a freshly prepared WC reveals the presence of a small amount of WO3 on the surface and a slightly higher concentration in the bulk. The oxygen-exposed fresh WC surfaces and surfaces treated at temperatures higher than 373 K show the presence of WO3 in a considerable quantity depending on the length and the treatment temperature. Ar+ bombardment of this partially oxidized surface reduces WO3 to WO2 and W(0), while WC is partially reduced to W(0). Isomerization reactions of alkanes on oxygen-exposed WC surface occurs in reality on a composite surface structure containing WC, WO3, WO2 and elemental W(0).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00807119
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  • 6
    Electronic Resource
    Electronic Resource
    Molybdenum based catalysts. I. MoO2 as the active species in the reforming of hydrocarbons (1996)
    Springer
    Catalysis letters 38 (1996), S. 95-99 
    Details
    ISSN: 1572-879X
    Keywords: molybdenum dioxide ; XPS ; argon ion bombardment ; reforming of alkanes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The XPS spectra of bulk MoO2 and MoO3 are reported. Commercial MoO2 reveals the presence of multilayers of MoO3 covering bulk MoO2. In situ reduction of bulk MoO3 by H2 at temperatures equal to 623 K and less than 673 K reduces the superficial layer(s) to mainly MoO2. Such phase is characterised by a certain density of states in terms of the free 4d, 5s electrons localised mainly on the Mo atoms and observed in the valence band energy region at the Fermi-level in the XP spectrum of this system. Catalytic reactions on the MoO2 phase of 2-methylpentane at atmospheric pressure using a mixture of the hydrocarbon (5 Torr) with hydrogen (755 Torr) yield 3-methylpentane andn-hexane as the main products in roughly equal amounts. These results are interpreted in terms of dual sites on the MoO2 surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00806906
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  • 7
    Electronic Resource
    Electronic Resource
    Monodispersed colloidal metal particles from nonaqueous solutions: Catalytic behaviour in hydrogenolysis and isomerization of hydrocarbons of supported platinum particles (1991)
    Springer
    Catalysis letters 9 (1991), S. 347-354 
    Details
    ISSN: 1572-879X
    Keywords: Catalysis ; platinum ; microemulsion ; isomerisation ; hydrogenolysis ; hexanes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Platinum catalysts have been prepared by depositing on alumina monodispersed particles of platinum prepared in reversed micellar solution. After deposition, the particles are well dispersed on the support and the size distribution has a sharp maximum around 2 nm. The isomerization and hydrogenolysis of hexanes were studied in order to get more information about the particle size effects on the selectivities of Pt catalysts in these reactions. It was found that this catalyst exhibits the same selectivities as a low dispersed ordinary platinum catalyst. These selectivity values are quite different from the ones given by a highly dispersed classical catalyst in spite of the fact that the catalysts have fairly similar average particle size. Such results confirm the conclusions previously proposed that isomerisation via cyclic mechanism and non selective hydrogenolysis of hexanes take place only on platinum particles smaller than 1 nm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00764825
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  • 8
    Electronic Resource
    Electronic Resource
    Catalytic behaviour of polycrystalline Pt3Ti in relation to strong metal-support interaction phenomenon (1989)
    Springer
    Catalysis letters 2 (1989), S. 139-144 
    Details
    ISSN: 1572-879X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Skeletal isomerization reactions, of hexanes (2-methylpentane and methylcyclopentane) have been carried out in a flow reactor on a polycrystalline intermetallic Pt3Ti compound which has been powdered and treated under several oxidative and reductive conditions. The results are compared to those obtained with (i) TiO2 supported Pt catalysts in or not in the Strong Metal-Support Interaction (SMSI) state, (ii) a bulk Pt3Ti sample studied under static catalytic conditions in an U.H.V. apparatus, and (iii) bulk Pt surfaces. The powdered Pt3Ti compound shows a very unstable behaviour under hydrogen. Differences in behaviour between the bulk and the decomposed powdered Pt3Ti samples are observed, showing the important part played by Pt3Ti in SMSI phenomena. A model is then proposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00775062
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  • 9
    Electronic Resource
    Electronic Resource
    Palladium particles growth on various aluminas (1989)
    Springer
    The European physical journal 12 (1989), S. 19-22 
    Details
    ISSN: 1434-6079
    Keywords: 79.60
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Pd was deposited from a filament onto anα-Al2O3 single-crystal. The Pd 3dP 5/2 binding energy change versus deposition time was used as a calibration of the Pd clusters size. The experiment was then reproduced onγ-Al2O3. The Pd 3d 5/2 binding energy showed that the clusters growth mechanism was now different. Thermal treatments produced a dispersion of the metal or a clusters size increase depending on the temperature or the nature of the support. Oxygen exposure dispersed Pd in every case. A mechanism is proposed to interpret this phenomenon.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01426897
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  • 10
    Electronic Resource
    Electronic Resource
    Geometric effects in methylcyclopentane hydrogenolysis on platinum catalysts (1982)
    Springer
    Reaction kinetics and catalysis letters 21 (1982), S. 219-224 
    Details
    ISSN: 1588-2837
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Abstract Гидрогенолиз метилциклопентана изучен при 493 К на платиновых катализаторах с различной дисперсностью. Относительные вклады доминирующих механизмов гидрогенолиза коррелируются с размерами частиц согласно простой геометрической модели.
    Notes: Abstract Methylcyclopentane hydrogenolysis was studied at 493 K over variously dispersed platinum catalysts. The relative contributions of the predominant hydrogenolysis mechanisms are correlated to the particle size in agreement with a simple geometric model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02070614
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