Selective catalytic reduction of nitric oxide over vanadia grafted on titania. Influence of vanadia loading on structural and catalytic properties of catalysts

The selective catalytic reduction (SCR) of NO by NH₃ has been studied over vanadia/ titania catalysts prepared by selective immobilization of vanadyl alkoxide species on two structurally different titania supports. The loading of vanadia was varied from 1.8 to 7.5 ,mol V⁵⁺ per m² surface area. Comparative kinetic measurements at 150 °C show that the NO turnover frequencies increase by more than an order of magnitude when the vanadia loading is increased from 1.8 to 3 mol V⁵⁺/m². In the region of lower SCR activity, i.e. at lower coverages ( 2 mol V⁵⁺/m²), small clusters and ribbons of vanadia are detected in the Raman spectra, whereas at loadings where maximum NO turnovers are achieved ( 3 mol V⁵⁺/m²) the prevalent vanadia species are well-developed two-dimensional vanadia layers bound to titania.