(691a) Enhanced Metal-Support Interaction of Flame Synthesized Pd/CeO2 Catalysts for Methane Oxidation | AIChE

(691a) Enhanced Metal-Support Interaction of Flame Synthesized Pd/CeO2 Catalysts for Methane Oxidation


Najimu, M. - Presenter, University of California Irvine
Sasmaz, E., University of California, Irvine
Kim, S., University of California, Irvine
Wang, C., University of California-Irvine
Palladium supported on reducible oxides are important class of catalysts for low-temperature CO and hydrocarbon oxidation reactions for vehicle emissions control. In this study, we focus on investigating how the dynamic behavior of Pd/CeO2 catalysts synthesized at different flame spray pyrolysis (FSP) synthesis conditions can influence the catalytic activity for CH4 oxidation. The 1wt% Pd/CeO2 catalysts synthesized at equivalence ratio (ER) of 0.8 and 1.5 show highly dispersed Pd species. In-situ DRIFTS experiments performed with CO at room temperature show that highly dispersed Pdn+ species exist on both ER-0.8 and -1.5 samples initially. However, Pdn+ can be reduced to highly dispersed Pd0 after CO interaction, which could consequently agglomerate to form larger Pd cluster species. The larger Pd0 clusters are more pronounced in the ER-1.5 sample compared to the ER-0.8. Hydrogen reduction experiments show that Pd species on both catalysts can be reduced at about 60 oC, yet species on the ER-0.8 catalyst have lower amount of reducible oxygen.

The ER-0.8 catalyst demonstrates a lower T50 conversion than the ER-1.5 catalyst for CH4 oxidation between 300 and 800oC reaction temperature. Since Pdn+ is shown to be active for CH4 oxidation in this temperature range, agglomeration of the Pd0 to Pd0 clusters on the ER-1.5 catalyst could be responsible for its lower methane oxidation activity. It is possible that the ER-0.8 demonstrates higher activity for CH4 oxidation due to the continuous reoxidation of the reduced Pd0 by the ceria lattice oxygen, since it does not undergo clustering. This reoxidation behavior might be due to the strong interaction of the Pdn+ species with CeO2 and can be controlled with the oxidizing environment provided at low ER during FSP. A detailed analysis of the effect of the synthesis condition on metal-support interaction will be provided.