Effects of tungsten on vanadium-based catalysts were studied under differently dispersed conditions of tungsten oxide on titania surface. Acidity, surface species and NH3-SCR performance over commercial WO3/TiO2 and V2O5-WO3/TiO2 have been investigated. The incomplete dispersion of tungsten oxide gives rise to the formation of crystalline WO3 on titania surface, and the mounts of surface Bronsted acid sites decrease consequently. From the TPR and Raman spectra, it is indicated that two-dimensional vanadium species exhibits a tendency to moderately anchor onto titania surface in the immediate vicinity of tungsten species. It is also found that amorphous tungsten oxide has different impacts on the dispersion of vanadium species over titania surface at variable loadings of vanadia. At low vanadium loadings, amorphously distorted tungsten species show promoting effects on the formation and dispersion of two-dimensional vanadium species. With vanadium loadings increasing, amorphous tungsten species exert compressing effects on surface vanadium species and lead to the aggregation of vanadium oxide. (c) 2013 Elsevier B.V. All rights reserved.