Calorimetric heats for CO and oxygen adsorption and for the catalytic CO oxidation reaction on Pt111

Single crystal adsorption calorimetry was applied to investigate the heats of adsorption of CO and oxygen and the reaction heats for the CO oxidation process on Pt111 at room temperature. Both sticking probabilities and heats of adsorption for CO and oxygen are presented as a function of coverage. These results are used to interpret the subsequent measurements taken for the CO oxidation process on the same surface. The initial heats of adsorption of CO and oxygen on Pt111 are 180±8 and 339±32 kJ/mol, respectively. In addition the pairwise lateral repulsive interaction between CO molecules in a (√3×√3) R30° ordered layer at θ=1/3 is found to be 4 kJ/mol. A detailed Monte Carlo modeling of the dissociative adsorption and sticking probability of oxygen on Pt111 is performed. The initial rapid fall in heat is attributed to adsorption on defect sites, and subsequent adsorption on the planar 111 surface proceeds with a third neighbor interaction energy between the oxygen adatoms ω3∼22 kJ/mol. When gaseous CO reacts with preadsorbed oxygen adatoms, the CO2 produced has an excess energy of 16±8 kJ/mol.