Tracer studies on the reaction path and kinetics of the Co oxidation over iridium

The reaction path and kinetics of the CO oxidation over polycrystalline indium were studied under low pressures by a transient isotope tracer method. Carbon monoxide is oxidized entirely through a Langmuir-Hinshelwood (LH) process, namely CO(a) + O(a) → CO₂. No evidence of an Eley-Rideal process, namely CO(g) + O(a) → CO₂, was observed. At constant temperatures the apparent rate constant of the LH process, i.e., the CO₂ formation rate divided by the product of the coverages of CO and oxygen, decreased rapidly with an increase in the total coverage. The kinetics was explained in terms of the boundary reaction model in which the oxidation took place predominantly outside or near the boundary of the CO(a) island.