Selective catalytic reduction of NO by ammonia over Raney-Ni supported Cu-ZSM-5 II. Interactions between support and supported Cu-ZSM-5

The selective catalytic reduction (SCR) of NO by NH3 was studied with compo site catalysts containing Cu-ZSM-5 supported on the surface of Raney-Ni and with an unsupported Cu-ZSM-5 reference catalyst. Particular attention was paid to the durability of the catalyst under severe treatments. A parallel study with the propene reductant was made to substantiate trends observed w ith ammonia. The composite catalysts are highly active with the ammonia red uctant, but exhibit also considerable activity with propene. Thermal stress at temperatures of approximate to 870 K (high-temperature use, steaming tr eatment) affects the composites in a different way than the unsupported ref erence catalyst, which provides lower NO conversions over the whole range o f temperatures studied (570-870 K). With the composite, NO conversions were decreased only at low reaction temperatures while they remained constant o r even improved at high temperatures. This was ascribed to migration of Ni ions into the zeolite (solid-state ion exchange) with concomitant stabilisa tion of the lattice. Thermal treatment at 1123 K destroyed both composite a nd unsupported Cu-ZSM-5. (C) 2000 Elsevier Science B.V. All rights reserved .