The role of water for NO reduction by hydrocarbons over copper ion-exchanged mordenite type zeolite catalysts

Abstract

The mordenite type natural zeolite catalyst(CuNZA) reveals more stable activity maintenance than the synthetic mordenite catalysts(HM and CuHM) in the presence of water vapor. From the XANES and EXAFS spectra of copper ion-exchanged catalysts, a chemical alteration of copper ions was not attributed to the activity loss by water, since no sintering of copper ions occurs even for the catalysts exposed to the wet stream. The deteriorating trends of the catalysts are well elucidated by the hydrophobicity of the catalyst surface. The amounts of NO adsorption on HM and CuHM catalysts are dramatically decreased due to the competitive adsorption of NO and H2O, but not on CuNZA catalyst. It reveals that the inhibition of NO adsorption sites by water is one of the crucial reasons of the activity loss for NO reduction by H2O. The contribution of the side reactions to the decrease of NO conversion by H2O, however may not be eliminated for this reaction system.