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  • Wiley-Blackwell  (7)
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  • 1
    Electronic Resource
    Electronic Resource
    Fine structure of supported and promoted catalysts as deduced from XPS intensity data (1992)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 19 (1992), S. 586-590 
    Details
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: For model calculations it is assumed that metal spheroids are randomly distributed on spherical support particles of nearly closest-packed arrangement. Both the metal and the support can be covered with layers or submonolayers of promoter(s) and carbon. The average diameters as well as n, the average number of metal particles on one support sphere, are estimated from total surface area and selective chemisorption measurements and preferably by electron microscopy too. In the computer programme two cases are distinguished depending on whether n 〈 4 or n 〉 4, since in the latter case the partial shadowing of coated metal particles by others should also be considered. Electron beams emitted by the metal, the support and their layers are calculated as a function of the ‘angle of latitude’ of the support spheres and the ‘angle of latitude and longitude’ of the metal spheroids. The computation variables are the thickness and sequence of different layers above the metal and the support, the extent of ‘immersion’ of metal particles into the support and/or its layers and the extent of diffusion of promotor cations into the support matrix. The calculated intensities are compared with the measured ones. By this method the probable fine structure of an alkali-promoted Pd/SiO2 (n 〈 4) and a sodium-promoted Ni/(Al2O3 + SiO2) catalyst (n 〉 4) has been determined.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/sia.7401901109
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  • 2
    Electronic Resource
    Electronic Resource
    Properties of surface-modified alumina catalysts of COS synthesis (1992)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 19 (1992), S. 529-532 
    Details
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The surface electronic structure, the acid-base properties, the component adsorption and the catalytic activity of gamma alumina (CK-300, Ketjen) modified with surface sodium as a donor-type or iron as an acceptor-type additive have been investigated. Alumina was loaded with 0.1 and 1 wt.% Na and Fe. The catalytic O/S exchange of CO2 and CS2 to form COS was applied as a model reaction, for which the kinetic parameters have also been determined. In the case of unloaded alumina and samples loaded with 0.1 wt.% Na and 0.1 or 1.0% Fe no characteristic differences in the shape and position of the O 1s and Al 2p lines were observed. However, 1.0 wt.% Na loading resulted in a broadening of the O 1s and Al 2p lines towards lower binding energies. Sodium, even in 1% monolayer coverage, and other donor-type surface species, e.g. pre-adsorbed NH3 or pyridine, exhibited a readily detectable promoter effect which could be characterized by increased surface basicity, increased CO2 and CS2 adsorption and better catalytic performance. In contrast, on catalysts loaded with Fe an increase in surface acidic sites, a loss of basic sites, decreased component adsorption and lower catalytic activity were observed.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/sia.740190198
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  • 3
    Electronic Resource
    Electronic Resource
    Surface characterization of the deactivation of alumina catalysts used for COS synthesis (1988)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 12 (1988), S. 262-268 
    Details
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: One of the possible routes of producing COS, an important material in organic synthese, is the CO2 + CS2 ⇄ 2COS reaction, preferably over gamma-alumina catalysts. Under long-term loading, however, a remarkable loss of the catalytic activity occurs.The nature of the ageing process was studied by a multi-technique apporach on high purity [I] and on a commerical grade [II] gamma-alumina, which latter contained Na, Ca, and S as surface impurities.On catalyst [I] weak chemisorption of CO2, CS2 and COS was observed by the volumetric method, as characterized by the isosteric heats of adsorption. Catalyst [II] chemisorbed CO2 and COS but not CS2 and showed much less catalytic activity. Gravimetric measurements have shown that adsorption of CS2 and COS leads to the surface deposition of side products. XPS studies on new, loaded and aged samples have revealed that the ageing of the catalyst is primarily caused by the deposition of sulphur and carbon with carbon in excess, presumably in C—S, C—S and C—C environements.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/sia.740120407
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  • 4
    Electronic Resource
    Electronic Resource
    Surface characterization of chlorine treated γ-Al2O3 catalysts (1988)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 12 (1988), S. 275-276 
    Details
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/sia.740120411
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  • 5
    Electronic Resource
    Electronic Resource
    Electronic state and catalytic activity of SiO2 doped γ-Al2O3 (1986)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 9 (1986), S. 237-241 
    Details
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Silica-alumina catalysts have been applied for a long time in cracking and reforming reactions. Lewis type surface sites are generally accepted to serve as active centers. In this respect, surface properties of these materials are of main concern. In the present work SiO2 doped γ-Al2O3 with less than a monolayer coverage were prepared by the reaction of SiCl4 (g) with γ-Al2O3 at 820-1120 K. Catalytic activity of the samples was tested by a model reaction of n-hexane cracking. Surface composition and electronic state were evaluated by XPS investigations performed on a KRATOS XSAM 800 instrument. Catalytic activity (conversion) varies remarkably with increasing Si content showing a sharp maximum at low Si coverage. The observed shift of Al 2p lines with increasing Si content is interpreted as an enhancement of the acceptor or acidic character of the surface Al atoms. The Auger parameter for Si(α'Si), (composed by addition of Si 2p BE and Si (KLL) KE values) passes also through a maximum at the same Si-content, as does the conversion curve. A close correlation of the Auger parameter and the catalytic activity is established for samples with (Si/Al)≲7%. This leads to a conclusion, that the rise in extra-atomic relaxation energy may serve as an additional indication of enhanced catalytic activity.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/sia.740090407
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  • 6
    Electronic Resource
    Electronic Resource
    XPS studies on doped vanadia catalysts in CO oxidation (1986)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 9 (1986), S. 260-260 
    Details
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/sia.740090418
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  • 7
    Electronic Resource
    Electronic Resource
    XPS characterization of ultrafine Si3N4 powders (1988)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 12 (1988), S. 527-530 
    Details
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The mechanical properties of Si3N4 based ceramic bodies are largely controlled by the phases formed on the grain boundaries during sintering. For this reason determination of the state and the chemical composition of the surface of the starting Si3N4 powder is of prime theoretial and practical importance, especially in the cases when advanced ultrafine powders are used. In this work an ultrafine Si3N4 powder, obtained by high temperature plasma nitridation of silicon, has been characterized by XPS. Oxygen, carbon and also a small amount of potassium were detected as surface impurities. The Si 2p and Si (KLL) spectral lines could be decomposed into two components corresponding to silicon in Si3N4 and SiO2 phases. From angle-resolved and Ar-ion depth-profiling experiments a layer model, consisting of a Si3N4 core covered by a relatively thick SiO2 layer and a carbon contaminant overlayer, could be elucidated.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/sia.740121004
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