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-mu-mol V5+ per m2 surface area. Comparative kinetic measurements at 150-degrees-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 almost-equal-to 3-mu-mol V5+/m2. In the region of lower SCR activity, i.e. at lower coverages (almost-equal-to 2-mu-mol V5+/m2), small clusters and ribbons of vanadia are detected in the Raman spectra, whereas at loadings where maximum NO turnovers are achieved (almost-equal-to 3-mu-mol V5+/m2) the prevalent vanadia species are well-developed two-dimensional vanadia layers bound to titania.