Selective Reduction of Nitric Oxide with Methane on Gallium and Indium Containing H-ZSM-5 Catalysts: Formation of Active Sites by Solid-State Ion Exchange

Abstract

H-ZSM-5 catalysts containing Ga and In were prepared by the ion-exchange method and by physically mixing H-ZSM-5 and Ga2O3or In2O3, and they were used in the NO reduction with methane to determine the active species of these metals, particularly of In, for this reaction. Ga-loaded H-ZSM-5 prepared by the ion-exchange method gave a higher catalytic activity than the physical mixture of Ga2O3and H-ZSM-5, of which the catalytic activity was comparable to that of H-ZSM-5. On the contrary, both ion-exchange and physical mixing methods yielded equally high catalytic activities of In-loaded H-ZSM-5. The reduction of NO on these catalysts proceeds consecutively by way of oxidation of NO to NO2and reduction of NO2with CH4to N2. With increasing heat treatment temperature, the catalytic activity of the mixture of In2O3and H-ZSM-5 for the reduction of NO2increased, while that for NO oxidation decreased. An IR study of OH groups on this catalyst indicated that the solid-state exchange reaction occurred between In2O3and H-ZSM-5 leading to the increase in the number of indium cation sites and consequently the catalytic activity for NO2reduction.