Intrapore catalysis in reduction of nitric oxide with methane

Catalytic activities of In/H-ZSM-5 and Ir/In/H-ZSM-5 for selective reduction of NO with methane were investigated with in situ measurements of NOx adspecies by FT-IR method under reaction conditions. The reaction proceeded in the following two stages: NO was oxidized to NO2 on Ir and NO2 was reduced to N-2 by CH4 on InO+. Studies on chemisorption of NOx indicated that NO2 chemisorbed on InO+ sites is important for this reaction. Two intense NO2 adspecies were observed at 1610 and 1575 cm(-1) under the reaction conditions: one of these species at 1610 cm(-1) is reactive with CH4. These adspecies are assigned to nitro or nitrite species. Nitrates adsorbed on InO+ (1450 cm(-1)) and zeolite acid sites (1635 cm(-1)) cannot consume CH4. Chemisorption of NO2 on InO+ sites were shown by IR measurements to be a slow step on In/H-ZSM-5, while Lr accelerated the chemisorption of NO2 on InO+ not only on the outer surface but also in the pores of ZSM-5. It is concluded that bifunctional catalysis in identical zeolite pores, named "intrapore catalysis", brings forth high catalytic activity and selectivity. (C) 1998 Elsevier Science B.V. All rights reserved.