Role of zeolite structure on reduction of NOx with methane over In- and Pd-based catalysts

Abstract Catalytic performances of ZSM-5 based catalysts containing indium or palladium were examined for NO reduction with CH 4 and NO x chemisorption. The amounts of NO x chemisorbed on In/H-ZSM-5 were well proportional to the catalytic activities for NO x reduction. Pd/H-ZSM-5, on the other hand, hardly chemisorbed NO 2 , while the catalytic activity for NO 2 reduction with CH 4 is very high. Furthermore, Pd loaded on SiO 2 showed comparably high catalytic activity for NO 2 reduction with CH 4 at 400°C in the absence of oxygen as Pd/H-ZSM-5. CH 4 combustion during NO x reduction with CH 4 in the presence of oxygen significantly occurred over PdO on SiO 2 , while less over Pd/H-ZSM-5. The role of zeolite might be slightly different between In/H-ZSM-5 and Pd/H-ZSM-5: the zeolitic porous structure is needed for In/H-ZSM-5 in order to concentrate NO 2 adspecies on InO + sites, which is important for NO reduction with CH 4 on In/H-ZSM-5 based catalysts, while the ion-exchangeable ability of zeolite is needed for Pd/H-ZSM-5 in order to make Pd 2+ located in a highly dispersed state, on which NO is strongly chemisorbed.

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