Selective Catalytic Realaction of Nitric Oxide with Hydrocarbons in Oxygen-rich Atmosphere

研究了在沸石催化剂上甲烷选择性还原NO的反应。考察了不同阳离子交换沸石的催化性能，发现Ga-ZSM-5和In-ZSM-5对CH_4还原NO具有高活性和高选择性。我们还表明，这种反应是适度促进，甚至由H-型ZSM-5，丝光沸石，镁碱沸石。从Ga-ZSM-5和In-ZSM-5对NO-CH_4-O_2、NO_2-CH_4-O_2和NO-O_2反应的催化性能来看，NO在这些催化剂上的选择性还原反应是分两个阶段进行的：（1）NO在沸石酸中心上氧化为NO_2;（2）NO_2和CH_4在镓或铟中心上反应。Ga和In在分子筛中对NO_2-CH_4反应的高选择性是由于Ga和In的配位不饱和性质，使它们吸附在同一位置上。研究了水蒸气对NO转化率的影响。结果表明，Ga-ZSM-5分子筛在水蒸气存在下具有很强的阻化作用，而In-ZSM-5分子筛在10%水蒸气存在下仍具有一定的活性。

Selective reduction of No by CH_4 on zeolite catalysts has been studied. After investigation on the catalytic features of various cation-exchaged 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-5in NO-CH_4-O_2, NO_2-CH_4-O_2, and NO-O_2 reactions, it is conuluded 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 zeolite for 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.