The selective catalytic reduction (SCR) of NO by NH3 was studied with composite 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 with ammonia. The composite catalysts are highly active with the ammonia reductant, but exhibit also considerable activity with propene. Thermal stress at temperatures of approximate to 870 K (high-temperature use, steaming treatment) affects the composites in a different way than the unsupported reference catalyst, which provides lower NO conversions over the whole range of temperatures studied (570-870 K). With the composite, NO conversions were decreased only at low reaction temperatures while they remained constant or even improved at high temperatures. This was ascribed to migration of Ni ions into the zeolite (solid-state ion exchange) with concomitant stabilisation of the lattice. Thermal treatment at 1123 K destroyed both composite and unsupported Cu-ZSM-5. (C) 2000 Elsevier Science B.V. All rights reserved.