CO OXIDATION ON LACOO3 PEROVSKITE

A study of CO oxidation on LaCoO3 perovskite was performed in an ultra high vacuum system by means of adsorption and desorption. All gases we re adsorbed at ambient temperature. Two adsorption states (alpha- and beta-) of CO exist. The alpha-peak at 440 K is attributed to carbonyl species adsorbed on Co3+ ions while the beta-peak at 663 K likely come s from bidentate carbonate formed by adsorption on lattice oxygens. CO 2 shows a single desorption peak (beta-state, 483 K) whose chemical st ate may be monodentate carbonate. A new CO2 desorption peak at 590 K c an be created by oxidation of CO. O2 also shows two adsorption states. One desorbs at 600 K, which may reflect adsorption on Co3+ ions. The other apparently incorporates with bulk LaCoO3 and desorbs above 1000 K. The two adsorption states of CO are oxidized via different mechanis ms. The rate determining step in oxidation of alpha-CO is the surface reaction whereas for that of beta-CO, it is desorption of product CO2.