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

Abstract 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 on pre-treatment conditions. Catalysts derived by grafting both transition metals (CrO x –VO x /TiO 2 ) as well as corresponding titania-supported single oxide catalysts, VO x /TiO 2 and CrO x /TiO 2 , were investigated in the selective catalytic reduction of nitric oxide by ammonia. The catalytic properties of CrO x –VO x /TiO 2 could be explained by the superimposed characteristic behaviours (activity, temperature range, selectivity) of the reference systems VO x /TiO 2 and CrO x /TiO 2 . Neither catalytic nor spectroscopic investigations indicated any interaction between grafted VO x and CrO x .