MECHANISM OF CO OXIDATION OVER POLYCRYSTALLINE PLATINUM

The kinetics of the CO oxidation has been studied on polycrystalline platinum at various partial pressures, total pressures, and temperatures. The reaction was first-order in CO and zero-order in O//2 for low pressures of CO, while it was inhibited by CO above a certain critical CO pressure, which increased with an increase in the O//2 pressure and temperature. Above that CO pressure, the reaction was first-order in O//2 and negative-order in CO. The amount of CO adsorbed was determined during the reaction with a flash-desorption technique. Above the critical CO pressure it was almost equal to that determined in the CO/Pt equilibrium system. It decreased sharply around the CO pressure and was very small at lower pressures. The kinetic behavior can be explained in terms of a Langmuir-Hinshelwood process and a change in the rate-limiting step.