Activity of palladium loaded on zeolites in the combustion of methane

Activity of Pd loaded on zeolite for the methane combustion was examined using various kinds of mordenite and ZSM-5 zeolites with different compositions of aluminum and cation. The activity strongly depended on the composition as well as on the structure of zeolites. Among tested catalysts, the highest and durable activity was found on the catalyst which was prepared from an ion exchange with palladium amine complex on the H-type siliceous mordenite such as Pd/H-mordenite (Si/Al-2=145). Reaction orders with respect to the partial pressures of methane and oxygen indicated that the oxidized form of palladium was the active species. Characterization using TEM and XPS showed the high dispersion of palladium in the framework of zeolite. TPR using methane as a reductant showed that the high activity of Pd on the siliceous H-mordenite could be explained qualitatively and quantitatively; i.e., Pd was affected by the qualitative alteration caused by the induced effects by Al and Na cations, whereas the number of active oxygens on Pd was quantitatively enhanced in the zeolite, particularly mordenite. The micropores of zeolite may have a role in preventing the sintering into large particles to stabilize the activity. (C) 1997 Elsevier Science B.V.