The catalytic oxidation of NO to NO2 (NO-COX) and the selective catalytic reduction of NO to N2 by methane in the presence of excess oxygen (NO-SCR) was studied over zeolite In,H-, Co,H-, and Co,In,H-ZSM-5 catalysts. The catalysts were characterized by temperature-programmed H 2 reduction (H2-TPR) and operando DRIFT spectroscopy. The cobalt was present in the catalysts predominantly in Co-oxide clusters, whereas the charge of the zeolite framework was balanced by H+ and cationic indium species. The Brønsted acid sites promoted the NO-COX reaction; however, the Co-oxide clusters were much more active in this reaction. In absence of indium the catalysts were inactive in the NO-SCR reaction. The NO/NO2 mixture formed in the NO-COX reaction was shown to further react with the InO+/(InOH)2+-zeolite resulting in the simultaneous formation of InNO3 and NO+ species. The Co-oxide clusters increased the rate of NO2 generation and, thereby, the InNO3/NO+ formation. It was substantiated that an N-containing organic intermediate was obtained in the reaction of methane and nitrate group. Nitrogen was generated in the reaction between the obtained intermediate and the NO+. The catalytic cycle must have been closed by the oxidation of In+ to InO+/(InOH)2+ by the reactant mixture.
- Co,In,H-ZSM-5 catalyst
- NO-SCR by CH
ASJC Scopus subject areas
- Process Chemistry and Technology
- Physical and Theoretical Chemistry