Calorimetric heats for CO and oxygen adsorption and for the catalytic CO oxidation reaction on Pt{111}

Abstract

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 Pt{111} 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 Pt{111} 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 Pt{111} 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.