Selective catalytic reduction of NO by ammonia over Raney-Ni supported Cu-ZSM-5 I. Catalyst activity and stability

Composite materials containing Raney Ni and Cu-ZSM-5 are highly active cata lysts for the selective catalytic reduction (SCR) of NO by NH3. Their catal ytic properties were studied with particular attention to the influence of moisture and SO2 in the feed, and to effects of catalyst shaping operations . Composite materials (16-20 wt-% zeolite) were prepared by mixing the comp onents, with different degree of segregation in the resulting pressed parti cles, 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 NH3, 2 % O-2 in He, at 3-6.5 10(5) h(-1) (related to zeolite component). With physical mixtures, the catalytic behaviour strong ly depended on the mixing strategy, particles containing both Ni and zeolit e being inferior to mixed Ni-only and zeolite-only particles. The SCR activ ity was promoted by 2 % H2O in the feed, SO2 (200 ppm) was a moderate poiso n at low temperatures, but indifferent or slightly promoting at high temper atures. A catalyst prepared from ZSM-5 grown on Raney Ni, which was ranked intermediate in dry feed, was promoted to excellent performance in H2O and SO2 containing feed at T > 700 K and was stable for 38 h at 845 K. The resu lts suggest that SCR catalysts containing highly active zeolites should be produced avoiding shaping operations e.g. by use of zeolite crystallites gr own on wire packings.