COOPERATIVE ACTION OF PALLADIUM AND MANGANESE(III) OXIDE IN THE OXIDATION OF CARBON-MONOXIDE

Palladium (Pd) and manganese(III) oxide (Mn2O3) cooperated in the oxidation of CO to exhibit high catalytic activity; vapor-phase oxygen was incorporated mainly through Mn2O3, and Pd withdrew the oxygen from Mn2O3. IR analysis showed that CO was predominantly adsorbed on Pd and that the CO adsorbed on the oxidized state of Pd (Pd-n+-CO) was an important intermediate. The CO2 formed by the oxidation of CO was found to be present on Mn2O3 in the form of CO3. The rate of CO oxidation showed about first-order dependence on CO partial pressure and was independent of the oxygen concentration. Incorporation and activation of vapor-phase oxygen were not rate limiting due to the high affinity of Mn toward oxygen. A reaction path was proposed in which CO was first adsorbed on the oxidized state of Pd, followed by oxidation to form CO2. The CO2 migrated to the surface of Mn2O3 and was desorbed into the vapor phase. Thus the combination of the oxygen-providing ability of Mn2O3 and the inherent high activity of Pd resulted in the improved performance of this composite catalyst. (C) 1995 Academic Press, Inc.