Composite catalyst, used for reducing nitrogen oxides in I.C. engine exhaust gases, comprises redox-active cerium oxide species on outer surface of carrier, and indium-oxo species in carrier pores

摘要

Composite catalyst comprises redox-active CeOx species on the outer surface of a crystalline porous aluminum silicate as carrier, and an indium-oxo species on the inner surface, i.e. in the pores, of the carrier, and being Lewis acid active as well as redox-active. An Independent claim is also included for a process for the production of a composite catalyst comprising charging a suspended catalyst carrier in its H+- or NH+-form by precipitating In(OH)3 from an indium salt solution or by grinding with In2O3 and subsequently charging by precipitating cerium hydroxide from a cerium salt solution; or charging a suspended catalyst carrier in its H+- or NH+-form by precipitating indium hydroxide and cerium hydroxide from an aqueous indium salt solution and cerium salt solution or by grinding with In2O3 and CeO2; treating with a gaseous reductant at 300-600 deg C for 0.5-6 hours; and treating the reduced precursor with a gaseous oxidant at 300-600 deg C for 0.5-6 hours. Preferred Features: The ratio of the cerium species on the outer surface to the cerium species in the pores is at least 4: 1. The amount of CeOx species present is 4-20 wt.%. The CeOx species can be replaced with La2O3 and/or ZrO2. The crystalline porous aluminum silicate is a MFI zeolite, MOR zeolite and/or BEA zeolite.