Adsorption of Carbon Monoxide on Pd(111) and Palladium Model Catalysts
J. Catal., (1997)DOI: 10.1006/jcat.1997.1708
Abstract
The adsorption of carbon monoxide on Pd(111) and SiO2/Si(100)-supported
palladium particles, ranging in size from 1.5 to 9.5 nm, was investigated
with ellipsometry. By calibrating the sensitivity of the ellipsometric
parameter delta Sigma for the carbon monoxide coverage on Pd(111)
with LEED, ellipsometry could be used for a quantitative analysis
of the adsorption isotherms. The saturation coverage of carbon monoxide
appeared to be ~0.5 ML on all samples, with respect to the number
of surface atoms and within the temperature (400�540 K) and pressure
range (up to 1 Pa) studied. The initial isosteric heat of adsorption
was 148 pm 5 kJ/mol on all samples. The heat of adsorption decreased
with an increasing CO coverage. The decrease of the heat of adsorption
with an increasing CO coverage occurred in a similar way on all samples.
From these results we conclude that there are no particle size effects
with the adsorption of CO on SiO2/Si(100)-supported palladium particles.
Since other studies on the adsorption of CO on palladium model catalysts
do find a particle size effect, it is concluded that the particle
size effects are dependent on the support or that the observed particle
size effect is in fact a support effect.