Studies of the mechanism of NO reduction by CH{sub 4} over Co-ZSM-5

The mechanism of NO reduction by methane was investigated by means of in situ infrared spectroscopy and temperature-programmed desorption and reaction spectroscopy. Infrared spectroscop revealed the presence of bands for mononitrosyl and dinitrosyl species in the absence of O{sub 2}. In the presence of O{sub 2} the dinitrosyl is rapidly converted to nitroso species at room temperature. Both the nitrosyl and nitroso species are stable to desorption, decomposition, and reaction with CH{sub 4} for temperature of up to 623 K. At higher temperatures, the nitroso species react preferentially with CH{sub 4} to form N{sub 2}, CO{sub 2}, and H{sub 2}O-Co remains in the +2 oxidation state and does not undergo reduction to the +1 state, thereby inhibiting the decomposition of the dinitrosyls to form N{sub 2}O and facilitates the conversion of the dinitrosyls to NO{sub 2}. The elementary processes by which adsorbed NO{sub 2} reacts with CH{sub 4} and the role of hydroxyl radicals in the reduction of NO will be discussed.