MECHANISTIC STUDY OF NO REDUCTION WITH METHANE OVER CO2-5 CATALYSTS( MODIFIED ZSM)

NO reduction with methane over Co-ZSM-5 has been studied in an oxidizi ng atmosphere. Although the activity was reduced due to the poisoning of oxygen, NO decomposed over Co-ZSM-5 to nitrogen and oxygen in two d ifferent temperature ranges, 100-300 degrees C and > 400 degrees C. Th is suggests the presence of two types of Co2+ cations in ZSM-5. The ad sorption of NO, NO2 and CH4, as well as the reduction of NO with metha ne in O-2 were studied with in-situ diffuse reflectance Fourier-transf orm infrared spectroscopy (DRIFT). NO and methane molecules were only weakly adsorbed on Co-ZSM-5, and would desorb completely at the reacti on temperature. The presence of oxygen was found to enhance the NO int eraction with Co-ZSM-5, leading to the formation of adsorbed NO2 inter mediates. The adsorbed NO2 would activate methane molecules and yield hydrogen and methyl radicals, which could in turn react with NO2 to ge nerate nitromethane intermediates. A tentative reaction mechanism has been proposed to elucidate the production of N-2, N2O, H2O, formaldehy de and CO2.