Metal-Support Interaction at Palladium-Composite Manganese Oxide Interface and CO Oxidation Activity

Pd-loaded perovskite composite manganese oxide (Pd/AMnO3, A = Ca, Sr, La) catalysts were prepared by coprecipitation method, in order to reveal metal-support interaction (MSI). Particulate PdO with sizes of a few ten nanometers were randomly formed on CaMnO3. On the other hand, fibrous PdO with diameter approximately 20 nm was formed on LaMnO3. Both shape of PdO were formed on SrMnO3. HAXPES measurement showed a down shift of valence band of deposited PdO depending on the composite manganese oxide. Our characterization indicates that the MSI at Pd–AMnO3 interface affects not only the shape but the electronic structure of deposited PdO on AMnO3. The CO oxidation activity was in order of Pd/LaMnO3 > Pd/SrMnO3 > Pd/CaMnO3, which corresponds to the order of the PdO valence band shift trend. We proposed that the observed correlation between the valence band shift and the CO oxidation activity for Pd/AMnO3 can be understood in terms of the CO adsorption strength.