Equilibrated adsorption of CO on silica-supported Pt catalysts

Microcalorimetric and infrared spectroscopic studies of CO adsorption on Pt/SiO2 were conducted at temperatures from 298 to 673 K. The adsorption of CO on silica-supported Pt is equilibrated at 673 K, and the microcalorimetric and spectroscopic results obtained at this elevated temperature are in agreement with results reported for Pt(111) at 300 K. The heat of CO adsorption decreases with coverage from the initial value of 190-180 kJ/mol to 75 kJ/mol at the saturation CO coverage of 0.7 ML. Tn addition, the IR band for CO adsorbed on atop rites shifts to higher wavenumbers, and the ratio of integral absorbances of bridge-bonded and atop-bonded species changes with CO coverage. At temperatures lower than 673 K, the adsorption of CO on Pt/SiO2 is not equilibrated, and the microcalorimetric and IR spectroscopic data are essentially independent of the apparent CO coverage. A Monte Carlo simulation model was used to consolidate data for CO adsorption on Pt/SiO2 and Pt(111). The simulation was based on a set of parameters describing the energetics for the formation of atop- and bridge-bonded CO species on a clean surface and lateral pairwise interactions between these species on a two-dimensional hexagonal lattice representing a Pt(111) surface.