REACTIVITY AND PHYSICOCHEMICAL CHARACTERIZATION OF V2O5-WO3/TIO2 DE-NOX CATALYSTS

V2O5-WO3/TiO2 samples with compositions similar to those of commercial de-NOx catalysts (WO3 similar to 9% w/w, V2O5, < 3% w/w) are characterised by XRD, surface area and pore size distribution, Fourier transform infrared, laser Raman, W-vis diffuse reflectance, electron paramagnetic resonance spectroscopies, and catalytic tests in the reduction of NOx by NH3. The V2O5-WO3/TiO2 catalysts exhibit higher reactivity than the binary V2O5/TiO2 and WO3/TiO2 samples with the same metal loading, and the temperature window for the SCR reaction is greatly widened. The catalysts consist of anatase TiO2 and their morphological properties closely resemble that of WO3/TiO2 for (V + W) surface coverages lower than one. Monomeric vanadyls and wolframyls and polymeric WwOy groups are observed in the samples with low vanadia loadings that are apparently similar to those present on the surface of the binary oxide systems with comparable metal loadings. On increasing the vanadium loading, polyvanadate species are also formed. EPR, FTTR, FT-Raman, and UV-vis techniques indicate a strong electronic interaction between V and W oxide species at the surface of the TiO2 support. This interaction leads to a higher reducibility of the ternary sample with respect to the corresponding binary ones. A synergism between V and W oxide surface species is suggested, which accounts for the high reactivity of the ternary samples in the SCR reaction. It is suggested that the higher reducibility of the samples, due to the electronic interactions between V and W and the TiO2 support, is responsible for the higher reactivity of the ternary catalysts, particularly at low temperatures. (C) 1995 Academic Press, Inc.