ROLE OF ZEOLITE STRUCTURE ON REDUCTION OF NOX WITH METHANE OVER IN-BASED AND PD-BASED CATALYSTS

Catalytic performances of ZSM-5 based catalysts containing indium or p alladium were examined for NO reduction with CH4 and NOx chemisorption . The amounts of NOx chemisorbed on In/H-ZSM-5 were well proportional to the catalytic activities for NOx reduction. Pd/H-ZSM-5, an the othe r hand, hardly chemisorbed NO2, while the catalytic activity for NO2 r eduction with CH4 is very high. Furthermore, Pd loaded on SiO2 showed comparably high catalytic activity for NO2 reduction with CH4 at 400 d egrees C in the absence of oxygen as Pd/H-ZSM-5. CH4 combustion during NOx reduction with CH4 in the presence of oxygen significantly occurr ed over PdO on SiO2, while less over Pd/H-ZSM-5. The role of zeolite m ight be slightly different between In/H-ZSM-5 and Pd/H-ZSM-5: the zeol itic porous structure is needed for In/H-ZSM-5 in order to concentrate NO2 adspecies on InO+ sites, which is important for NO reduction with CH4 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 Pd2+ located in a highly dispersed state, on which NO is strongly chemisorbed. (C) 199 8 Elsevier Science B.V. All rights reserved.