IR mechanistic studies on NO reduction with NH3 in the presence of oxygen over cerium-exchanged mordenite

An in situ IR study on NO reduction with ammonia in the presence of oxygen has been performed with cerium-exchanged mordenite (CeNaMOR) in order to examine the reaction intermediates involved in the reaction. Go-adsorption of NO and O-2 on fresh CeNaMOR resulted in the formation of NO+ (nitrosonium ion: 2161 cm(-1)), NO2- (nitrito: 1416 cm(-1)) and NO3- (nitrate: 1510, 1487 and 1337 cm(-1)), while NH3 adsorption on fresh CeNaMOR led to the formation of NH4+ (1470, 1730, 2500-3500 cm(-1)) and coordinatively bonded NH3 species (1603, 2500-3500 cm(-1)). Under a how of the three reactants (NO, NH3 and O-2) as the case for the selective catalytic reduction (SCR) reaction in practice, the adsorbed ammonia species turned out to be dominantly present on CeNaMOR. The admission of NO and O-2 over NH3-preadsorbed CeNaMOR at 100 degrees C led to the preferred disappearance of coordinatively bonded NH3 species, prior to NH4+, and at the same time, the appearance of the bands due to water and NO2- was observed. The admission of NH3 at 100 degrees C over CeNaMOR containing preadsorbed NOx species (NO+, NO3- and NO2-) resulted in a substantial reduction of the NO+ band, while the NOx- species were found to disappear simultaneously with NH4+ only at and above 300 degrees C, leaving water as a product. Based on these results, a nitrosation reaction scheme is proposed, where NO+ and NH3 react easily, and the less reactive adsorbed species, NO2- and NH4+, react with each other only at a higher temperature. The proposed scheme can agree with the reaction stoichiometry and reaction orders known for NO reduction with NH3 over CeNaMOR.