Vanadia-chromia grafted on titania:: structural and catalytic properties in the selective catalytic reduction of NO by NH3

Chromia-vanadia on titania catalysts were prepared by sequential and simultaneous chemical reaction (grafting) of alkoxide and amide precursors of the transition metals with hydroxyl groups of the surface of titania. Their structure and redox properties under mild conditions were investigated by temperature programmed reduction by hydrogen (TPR) and spectroscopic methods, including UV-VIS and EPR. The oxidation state of the grafted transition metals depended strongly oh pre-treatment conditions. Catalysts derived by grafting both transition metals (CrOx-VOx/TiO2) as well as corresponding titania-supported single oxide catalysts, VOx/TiO2 and CrOx/TiO2, were investigated in the selective catalytic reduction of nitric oxide by ammonia. The catalytic properties of CrOx-VOx/TiO2 could be explained by the superimposed characteristic behaviours (activity, temperature range, selectivity) of the reference systems VOx/TiO2 and CrOx/TiO2. Neither catalytic nor spectroscopic investigations indicated any interaction between grafted VOx and CrO2. (C) 2000 Elsevier Science B.V. All rights reserved.