Kinetic studies on the CO oxidation over platinum by means of carbon 13 tracer

The kinetics of the CO oxidation over polycrystalline platinum was investigated with a transient isotope tracer method. Transient CO₂ production was generated by a dosage of various gas mixtures of ¹²CO and O₂ to the surface precovered by various ratios of ¹³CO to ¹²CO. The initial ratio of ¹³CO₂ to ¹²CO₂ in the CO₂ produced transiently equaled that of ¹³CO to ¹²CO in the CO preadsorbed for all the conditions studied; CO must be chemisorbed before being oxidized, i.e. a Langmuir-Hinshelwood mechanism is operative. The ratio of ¹³CO₂ to ¹²CO₂ in CO₂ decreased more rapid than the average ratio of ¹³CO(a) to ¹²CO(a) in CO(a). This apparent inhomogeneity in the reactivity of CO(a) was explained in terms of the boundary reaction model, in which the reaction took place predominantly outside or near the boundary of the CO(a) island.