Selective Catalytic Reduction of NO by Ammonia over Raney-Ni Supported Cu-ZSM-5 I. Catalyst Activity and Stability

Abstract

Composite materials containing Raney Ni and Cu-ZSM-5 are highly active catalysts for the selective catalytic reduction (SCR) of NO by NH 3 . Their catalytic properties were studied with particular attention to the influence of moisture and SO 2 in the feed, and to effects of catalyst shaping operations. Composite materials (16±20 wt-% zeolite) were prepared by mixing the components, with different degree of segregation in the resulting pressed particles, or by growing ZSM-5 crystallites on the surface of leached Raney Ni, which were then exchanged with Cu ions. Catalytic tests were performed with 1000 ppm NO, 1000 ppm NH 3 , 2 % O 2 in He, at 3±6.5 . 10 5 h ±1 (related to zeolite component). With physical mixtures, the catalytic behaviour strongly depended on the mixing strategy, particles containing both Ni and zeolite being inferior to mixed Ni-only and zeoliteonly particles. The SCR activity was promoted by 2 % H 2 O in the feed, SO 2 (200 ppm) was a moderate poison at low temperatures, but indifferent or slightly promoting at high temperatures. A catalyst prepared from ZSM-5 grown on Raney Ni, which was ranked intermediate in dry feed, was promoted to excellent performance in H 2 O and SO 2 containing feed at T > 700 K and was stable for 38 h at 845 K. The results suggest that SCR catalysts containing highly active zeolites should be produced avoiding shaping operations e.g. by use of zeolite crystallites grown on wire packings.