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On the porosity of coldly condensed sers active Ag films
A50 John L. F A L C O N E R Department of Chemical Engineering, Uni~,,er~iO, of Colorado. Boulder. Colorado 80309, USA Received 2 July 1984 A new method for model surface preparation of nickel/alumina catalysts, compatable with an ultrahigh vacuum environment, is described. The model system consists of a tungsten substrate, an evaporated aluminum film which is subsequently oxidized, and an evaporated, submonolayer coverage of nickel. This thin-film model has been used to study carbon monoxide methanation. The specific reaction rates and activation energy associated with this reaction compare favorably with the corresponding values found for high-area, supported nickel catalysts. Advantages and possible applications of the model system are discussed.
358
Surface Science 150 (1985) 358-366 North-Holland, Amsterdam
PARTICLE SIZE EFFECTS O N WULFF C O N S T R U C T I O N S L.D. M A R K S Department of Phvstcs, Artzona State Umverstty. Tempe, Art=ona 85287. USA Received 11 July 1984; accepted for publication 16 October 1984 The equilibrium structure of small particles is analysed by minimising the total surface energy of atomistic clusters. Large deviations from the bulk Wulff construction are identified for fairly large ( ~ 10 nm) particles due to sphere packing corrections. These act as additional edge terms which can be significantly larger than the true edge terms. For a simplified fcc model, it is shown that the fraction of (100) surface drops markedly as the particle size drops because of these packing effects. This can lead to very large particle size effects for a face sensitive catalytic reaction, it is also pointed out that these packing corrections link very small ( < 100 atom) cluster to very large particles.
Surface Science 150 (1985) 367-385 North-Holland. Amsterdam
367
O N THE P O R O S I T Y O! 7 COLDLY C O N D E N S E D SERS ACTIVE Ag FILMS I. Characterization of the films by means of Xe adsorption E.V. A L B A N O *, S. D A I S E R **, R. M I R A N D A *** a n d K. W A N D E L T lnstttut fur Phystkahsche Chemie, Universit~Jt Mfmchen. Sophienstrasse I1, D- 8000 M~nehen 2, Fed. Rep. of Germam' Received 15 August 1984; accepted for publication 9 October 1984 In this paper we report on the geometric structure of Ag films, deposited under UHV conditions and annealed at temperatures (Tan) ranging from 58 to 430 K, as deduced from UPS, AES, TDS and work function measurements of adsorbed xenon. The macroscopic work function
358
Surface Science 150 (1985) 358-366 North-Holland, Amsterdam
PARTICLE SIZE EFFECTS O N WULFF C O N S T R U C T I O N S L.D. M A R K S Department of Phvstcs, Artzona State Umverstty. Tempe, Art=ona 85287. USA Received 11 July 1984; accepted for publication 16 October 1984 The equilibrium structure of small particles is analysed by minimising the total surface energy of atomistic clusters. Large deviations from the bulk Wulff construction are identified for fairly large ( ~ 10 nm) particles due to sphere packing corrections. These act as additional edge terms which can be significantly larger than the true edge terms. For a simplified fcc model, it is shown that the fraction of (100) surface drops markedly as the particle size drops because of these packing effects. This can lead to very large particle size effects for a face sensitive catalytic reaction, it is also pointed out that these packing corrections link very small ( < 100 atom) cluster to very large particles.
Surface Science 150 (1985) 367-385 North-Holland. Amsterdam
367
O N THE P O R O S I T Y O! 7 COLDLY C O N D E N S E D SERS ACTIVE Ag FILMS I. Characterization of the films by means of Xe adsorption E.V. A L B A N O *, S. D A I S E R **, R. M I R A N D A *** a n d K. W A N D E L T lnstttut fur Phystkahsche Chemie, Universit~Jt Mfmchen. Sophienstrasse I1, D- 8000 M~nehen 2, Fed. Rep. of Germam' Received 15 August 1984; accepted for publication 9 October 1984 In this paper we report on the geometric structure of Ag films, deposited under UHV conditions and annealed at temperatures (Tan) ranging from 58 to 430 K, as deduced from UPS, AES, TDS and work function measurements of adsorbed xenon. The macroscopic work function