Reactivity of V2O5-WO3/TiO2 catalysts in the selective catalytic reduction of nitric oxide by ammonia

The physico-chemical characteristics and the reactivity of sub-monolayer V2O5-WO3/TiO2 deNO(x) catalysts is investigated in this work by EPR, FT-IR and reactivity tests under transient conditions. EPR indicates that tetravalent vanadium ions both in magnetically isolated form and in clustered, magnetically interacting form are present over the TiO2 surface. The presence of tungsten oxide stabilizes the surface V-IV and modifies the redox properties of V2O5/TiO2 samples. Ammonia adsorbs on the catalysts surface in the form of molecularly coordinated species and of ammonium ions. Upon heating, activation of ammonia via an amide species is apparent. V2O5-WO3/TiO2 catalysts exhibits higher activity than the binary V2O5/TIO2 and WO3/TiO2 reference sample. This is related to both higher redox properties and higher surface acidity of the ternary catalysts, Results suggest that the catalyst redox properties control the reactivity of the samples at low temperatures whereas the surface acidity plays an important role in the adsorption and activation of ammonia at high temperatures.