WEAKLY BOUND CARBON-MONOXIDE AT CATALYTICALLY ACTIVE-SITES ON CU(111)/PD(111) THIN-FILMS

被引:7
作者
VOOK, RW
ORAL, B
机构
[1] Laboratory for Solid State Science and Technology, Physics Department, Syracuse University, Syracuse
关键词
D O I
10.1016/0169-4332(92)90496-K
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
Epitaxial Cu(111)/Pd(111) thin films were formed on mica substrates by vacuum evaporation in UHV. The films were characterized by LEED, AES, thermal desorption spectroscopy (TDS), work-function (WF) change and their catalytic activities relative to that of a Pd(111) film. AES, WF, and TDS of CO adsorbates were used to show that Cu grew by atomic layers on epitaxial Pd(111) films formed on mica. LEED measurements indicated that the Cu overgrowth was epitaxial and that it was pseudomorphic with its Pd(111) substrate up to approximately 3-5 monolayers (ML) of Cu. TDS measurements on CO adsorption indicated that the saturation coverage dropped by approximately 25% for each 0.5 ML Cu that was deposited and that almost no CO adsorbed on 2 ML Cu/Pd bilayers. The WF change on CO adsorption, however, decreased much more rapidly as the Cu overlayer thickened, indicating that the charge transfer per CO molecule decreased correspondingly. The difference between the normalized TDS and WF change curves for saturation CO adsorption is a measure of the density of weakly bound (lower charge transfer) CO molecules on the bilayer surface. This difference curve peaks at 0.5 ML Cu. Catalytic activity measurements at atmospheric pressure for the CO oxidation reaction on these Cu(111)/Pd(111) bilayers had two peaks, one at 0.5 ML Cu and the other at 3 ML Cu. The peak at 0.5 ML Cu is shown to be due to catalytically active sites located in the vicinity of the edges of the monolayer high Cu islands. The peak at 3 ML Cu is due to the generation of misfit dislocations from threading dislocations which leave steps on the surface. The atomic displacements associated with the generation of these steps bring certain Cu atoms approximately 1 ML closer to Pd atoms, thereby increasing the catalysis rate at these steps. Further thickening of the Cu overlayer nullifies the effects of steps since Cu has a much lower activity than Pd.
引用
收藏
页码:681 / 687
页数:7
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共 20 条
  • [1] ONE-DIMENSIONAL DISLOCATIONS .1. STATIC THEORY
    FRANK, FC
    VANDERMERWE, JH
    [J]. PROCEEDINGS OF THE ROYAL SOCIETY OF LONDON SERIES A-MATHEMATICAL AND PHYSICAL SCIENCES, 1949, 198 (1053): : 205 - 216
  • [2] GRADMANN U, 1966, ANN PHYS-BERLIN, V17, P91
  • [3] HOUSTON JE, 1987, MRS S P, V83, P107
  • [4] EXPERIMENTAL-EVIDENCE FOR ROOM-TEMPERATURE INTERMETALLIC COMPOUND FORMATION AT THE PD/AL INTERFACE
    JIANG, LQ
    RUCKMAN, MW
    STRONGIN, M
    [J]. PHYSICAL REVIEW B, 1989, 39 (03): : 1564 - 1568
  • [5] Kaneyoshi T., 1991, INTRO SURFACE MAGNET
  • [6] THERMAL-DESORPTION SPECTROSCOPY INVESTIGATION OF CO ADSORPTION ON CU/PD(111) SURFACES
    ORAL, B
    LEE, YC
    VOOK, RW
    [J]. APPLIED SURFACE SCIENCE, 1990, 44 (01) : 65 - 73
  • [7] GROWTH MODE DETERMINATIONS FOR THE EPITAXIAL CU/PD(111)/MICA AND PD/CU(111)/MICA THIN-FILM SYSTEMS
    ORAL, B
    VOOK, RW
    [J]. JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A-VACUUM SURFACES AND FILMS, 1990, 8 (03): : 3048 - 3051
  • [8] KINETICS OF CO ADSORPTION ON EPITAXIAL (111)CU ON (111)PD THIN-FILMS
    ORAL, B
    KOTHARI, R
    VOOK, RW
    [J]. JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A-VACUUM SURFACES AND FILMS, 1989, 7 (03): : 2020 - 2023
  • [9] THERMAL-DESORPTION SPECTROSCOPY OF CO ADSORPTION ON EPITAXIAL CU(111)-PD(111) THIN-FILM SURFACES
    ORAL, B
    VOOK, RW
    [J]. VACUUM, 1990, 41 (1-3) : 227 - 229
  • [10] ORAL B, 1990, THESIS SYRACUSE U