H/D exchange of methane over transition metal/MFI catalysts Original Research Article

The H/D exchange of CH4 with D2 has been studied by on-line mass spectrometry over a series of transition metal/zeolite catalysts. Isotope exchange of CH4 with D2 is rapid over reduced Pd/MFI under conditions where no exchange can be detected over H/MFI, Cu/MFI or Fe/MFI. The exchange mechanism is stepwise, deuteromethanes are formed in ratios predicted by statistical thermodynamics. This reaction can be used as a catalytic probe to detect the presence of Pdn0 clusters. It shows that in the selective reduction of NO over Pd/MFI some Pd0 exists even in the presence of excess O2. On those Pd/MFI catalysts where Pdn0 particles and acidic protons coexist, the exchange of surface hydrons against D2 is strongly catalyzed by Pd0, temperature programmed reaction identifies two types of sites with different rate constants.