Methane Combustion over Pd Catalysts Loaded on Medium and Large Pore Zeolites

Methane combustion was conducted over Pd catalysts supported on medium (ZSM-5, ferrierite, TNU-9, TNU-10) and large (USY, mordenite, beta) pore zeolites. Among the catalysts studied here, Pd/H-TNU-10 exhibited the highest combustion activity, together with excellent durability in the presence of water vapor. A combination of TEM and Pd K-edge XAFS measurements reveals the formation of highly dispersed PdO particles within the TNU-10 pores. This is also the case of Pd/H-ferrierite, while frequently there are large particles (60-100 A...) on its outer surface. In contrast, most of PdO on zeolites other than these two medium pore materials were found to exist as aggregated particles (> 50 A...) on their outer crystallite surface. It appears that zeolite structures with intersecting 10- and 8-ring pores may be better supports for stabilizing nanometric PdO particles than those with the uniform 10-ring size or with the 12-ring pore system.