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Study of the growth mechanism of platinum layers on the Na0.7WO3(100) single crystal surface
A590 R.W. JOYNER
B.P. Research Centre, Chertsey Road, Sunbury-on-Thames, Middlesex TW16 7LN, UK Received 1 April 1985; accepted for publication 6 June 1985 Recent calculations have indicated that electronic factors play an important role in the poisoning of certain catalytic reactions. Although there is broad agreement on the general influence of poisons and promoters on local electronic structure, the lack of information on the reaction path means that the specific role of this electronic structure is not as well understood. We present calculations that illustrate the action of S and Li on the methanation of CO on Ni(100) and examine the effects of boundary conditions and self-consistency on the calculated electronic structures. We find that poisons exert a direct effect on the 5o level, with a much weaker influence on Er and the 27r*. Promoters, however, interact almost exclusively with the 2~r* near Ef, leading to a large shift towards Ef, and a large broadening.
Surface Science 162 (1985) 329-336 North-Holland, Amsterdam
329
A SURFACE COMPOSITION STUDY OF SULFIDED COBALT-MOLYBDENUM CATALYSTS BY LOW ENERGY ION SCATI'ERING J.-M. BEUKEN
SPECTROMETRY
(ISS)
a n d P. B E R T R A N D
Universitb Catholique de Louvain, PCPM, Place Croix de Sud 1, B-1348 Louvain-La-Neuve, Belgium Received 1 April 1985; accepted for publication 30 April 1985 Low energy ion scattering was used to analyse the surface composition of sulfided cobalt-molybdenum catalysts supported on ),-alumina powders (CoMoS/y-Al203). A method is proposed for the correct interpretation of the ISS spectra of this complex system. It is based on a curve synthesis procedure using the spectra obtained on pure phase materials (MoS2, Co9S8 and y-A1203). The results confirm a model of sintering of the MoS2 dispersed phase occurring when the samples are activated at a high reduction-sulfidation temperature.
Surface Science 162 (1985) 337-341 North-Holland, Amsterdam STUDY OF THE GROWTH
337 MECHANISM
OF PLATINUM
LAYERS ON
T H E Nao.TWOa(100) S I N G L E C R Y S T A L S U R F A C E U. B A R D I , A. S A N T U C C I
a n d G. R O V I D A
Dipartimento di Chimica, Universith di Firenze, 1-50121 Firenze, Italy Received 1 April 1985; accepted for publication 30 April 1985 Platinum supported on NaxWO 3 has interesting catalytic properties in the electrolytic reduction of oxygen in fuel cells. In the present work we investigated the structure of Pt layers deposited on the Na0.vWO3(100 ) surface by thermal evaporation or sputtering. Monitoring the intensity of the substrate and adsorbate AES signal, as well as the absorbed crystal current, it has been possible to determine that platimum grows on the substrate by the Frank-Van der Merwe (or layer-by-layer) growth mechanism.
B.P. Research Centre, Chertsey Road, Sunbury-on-Thames, Middlesex TW16 7LN, UK Received 1 April 1985; accepted for publication 6 June 1985 Recent calculations have indicated that electronic factors play an important role in the poisoning of certain catalytic reactions. Although there is broad agreement on the general influence of poisons and promoters on local electronic structure, the lack of information on the reaction path means that the specific role of this electronic structure is not as well understood. We present calculations that illustrate the action of S and Li on the methanation of CO on Ni(100) and examine the effects of boundary conditions and self-consistency on the calculated electronic structures. We find that poisons exert a direct effect on the 5o level, with a much weaker influence on Er and the 27r*. Promoters, however, interact almost exclusively with the 2~r* near Ef, leading to a large shift towards Ef, and a large broadening.
Surface Science 162 (1985) 329-336 North-Holland, Amsterdam
329
A SURFACE COMPOSITION STUDY OF SULFIDED COBALT-MOLYBDENUM CATALYSTS BY LOW ENERGY ION SCATI'ERING J.-M. BEUKEN
SPECTROMETRY
(ISS)
a n d P. B E R T R A N D
Universitb Catholique de Louvain, PCPM, Place Croix de Sud 1, B-1348 Louvain-La-Neuve, Belgium Received 1 April 1985; accepted for publication 30 April 1985 Low energy ion scattering was used to analyse the surface composition of sulfided cobalt-molybdenum catalysts supported on ),-alumina powders (CoMoS/y-Al203). A method is proposed for the correct interpretation of the ISS spectra of this complex system. It is based on a curve synthesis procedure using the spectra obtained on pure phase materials (MoS2, Co9S8 and y-A1203). The results confirm a model of sintering of the MoS2 dispersed phase occurring when the samples are activated at a high reduction-sulfidation temperature.
Surface Science 162 (1985) 337-341 North-Holland, Amsterdam STUDY OF THE GROWTH
337 MECHANISM
OF PLATINUM
LAYERS ON
T H E Nao.TWOa(100) S I N G L E C R Y S T A L S U R F A C E U. B A R D I , A. S A N T U C C I
a n d G. R O V I D A
Dipartimento di Chimica, Universith di Firenze, 1-50121 Firenze, Italy Received 1 April 1985; accepted for publication 30 April 1985 Platinum supported on NaxWO 3 has interesting catalytic properties in the electrolytic reduction of oxygen in fuel cells. In the present work we investigated the structure of Pt layers deposited on the Na0.vWO3(100 ) surface by thermal evaporation or sputtering. Monitoring the intensity of the substrate and adsorbate AES signal, as well as the absorbed crystal current, it has been possible to determine that platimum grows on the substrate by the Frank-Van der Merwe (or layer-by-layer) growth mechanism.