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

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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 an 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 ((V)3x(r)oot 3)R30 degrees ordered layer at theta=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 oil defect sites, and subsequent adsorption on the planar{111} surface proceeds with a third neighbor interaction energy between the oxygen adatoms omega(3) similar to 22 kJ/mol. When gaseous CO reacts with preadsorbed oxygen adatoms, the CO2 produced has an excess energy of 16+/-8 kJ/mol