Structural and chemisorptive properties of model catalysts: Copper supported on SiO[sub 2] thin films

Journal Article · Thu Jan 21 00:00:00 EST 1993 · Journal of Physical Chemistry; (United States)

OSTI ID:6202091

Xu, Xueping; Goodman, D W ^[1]

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1. Texas A M Univ., College Station (United States)

The structural and chemical properties of model silica-supported copper catalysts have been investigated with infrared reflection-absorption spectroscopy and temperature-programmed desorption using CO as a probe molecule. The isosteric heats of adsorption of carbon monoxide on the model catalysts were measured at pressures between 10[sup [minus]8] and 10[sup [minus]3] Torr and temperatures between 180 and 300 K. The model catalysts were prepared by evaporating copper onto a planar silica thin film ([approximately]100 [Angstrom]) which, in turn, was supported on a Mo(110) surface. When deposited at 100 K, copper initially forms a two-dimensional structure on silica; however, annealing induces the ultrathin copper films (< 3 ML) to form small clusters. The unannealed copper films have a significant density of low-coordinated copper sites, whereas the annealed films consist of copper clusters with structures similar to low-index [(111), (110)] and high-index copper planes [(211) or (311)]. The distribution of the facets depends upon the initial copper coverage. The dispersion of the copper on the planar silica films is high, [approximately]0.5, for the annealed films with [theta][sub Cu] < 2 ML. Carbon monoxide desorbs in a single peak centered at [approximately]210 K from the unannealed copper film, but in several peaks centered between 150 and 220 K from the annealed film. The CO adsorption energy strongly depends on the CO coverage, varying, from [approximately]17 kcal/mol at the low coverage limit to [approximately]10 kcal/mol near CO saturation. 38 refs., 12 figs., 1 tab.

• OSTI ID: 6202091
• Journal Information: Journal of Physical Chemistry; (United States), Vol. 97:3; ISSN 0022-3654
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
CARBON MONOXIDE
CHEMISORPTION
COPPER
ABSORPTION SPECTROSCOPY
SORPTIVE PROPERTIES
ABSORPTION HEAT
ANNEALING
CATALYST SUPPORTS
CATALYSTS
DESORPTION
MILLER INDICES
MOLECULAR STRUCTURE
MOLYBDENUM
SILICON OXIDES
THIN FILMS
CARBON COMPOUNDS
CARBON OXIDES
CHALCOGENIDES
CHEMICAL REACTIONS
ELEMENTS
ENERGY
ENTHALPY
FILMS
HEAT
HEAT TREATMENTS
METALS
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
SEPARATION PROCESSES
SILICON COMPOUNDS
SORPTION
SPECTROSCOPY
SURFACE PROPERTIES
THERMODYNAMIC PROPERTIES
TRANSITION ELEMENTS
400201* - Chemical &amp; Physicochemical Properties