Selective catalytic reduction of nitrogen monoxide by methane on zeolite catalysts in an oxygen-rich atmosphere

Abstract

Selective reduction of NO by CH 4 on zeolite catalysts has been studied. After an investigation of the catalytic features of various cation-exchanged zeolites, we found that Ga-ZSM-5 and In-ZSM-5 were highly active and selective for NO reduction by CH 4. We also showed that this reaction was moderately promoted even by H-form ZSM-5, mordenite, and ferrierite. From the catalytic performance of Ga-and In-ZSM-5 in NO-CH 4-O 2, NO 2-CH 4-O 2, and NO-O 2 reactions, it is concluded that the selective reduction of NO on these catalysts proceeds in two stages: (1) NO is oxidized to NO 2 on zeolite acid sites, (2) NO 2 and CH 4 react on gallium or indium sites. The highly selective features of Ga and In in the zeolite for the NO 2-CH 4 reaction seem to be attributed to the coordinatively unsaturated nature of these sites which adsorb both of these reactants on the same site. Effect of water vapor on NO conversion was also investigated. It was found that Ga-ZSM-5 was strongly inhibited by steam, while In-ZSM-5 was fairly active even in the presence of 10% steam.