SELECTIVE CATALYTIC REDUCTION OF NITROGEN-OXIDE BY HYDROCARBONS OVER MORDENITE-TYPE ZEOLITE CATALYSTS

Abstract

The reduction of NO by hydrocarbons such as C2H4, C2H6, C3H6, and C3H8 has been investigated over mordenite-type zeolite catalysts including HM, CuHM, NZA (natural zeolite), and CuNZA prepared by an ion-exchange method in a continuous how fixed-bed reactor. NO conversion over CuNZA catalyst reaches about 94% with 2000 ppm of C3H6 at 500 degrees C. As reductants, alkenes seem to exhibit a higher performance for NO conversion than alkanes regardless of the catalysts. No deterioration of the catalytic activity due to carbonaceous deposits for CuNZA was observed above 400 degrees C even after 30 h of on-stream time, but SO2 in the feed gas stream causes a severe poisoning of the CuNZA catalyst. The effect of H2(O) on NO conversion was significant regardless of the catalysts and the reductants employed in this study. However, CuNZA catalyst shows a unique water tolerance with C3H6. The reaction path of NO to N-2 is the most important factor for high performance of this catalytic system. NO is directly reduced by a reaction intermediate, Cn'Hm'(O) formed from hydro-carbon and O-2, N2O is another reaction intermediate which can be easily removed by Cn'Hm'(O).