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 characte rised by XRD, surface area and pore size distribution, Fourier transfo rm infrared, laser Raman, W-vis diffuse reflectance, electron paramagn etic resonance spectroscopies, and catalytic tests in the reduction of NOx by NH3. The V2O5-WO3/TiO2 catalysts exhibit higher reactivity tha n the binary V2O5/TiO2 and WO3/TiO2 samples with the same metal loadin g, and the temperature window for the SCR reaction is greatly widened. The catalysts consist of anatase TiO2 and their morphological propert ies closely resemble that of WO3/TiO2 for (V + W) surface coverages lo wer than one. Monomeric vanadyls and wolframyls and polymeric WwOy gro ups are observed in the samples with low vanadia loadings that are app arently similar to those present on the surface of the binary oxide sy stems with comparable metal loadings. On increasing the vanadium loadi ng, 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 l eads to a higher reducibility of the ternary sample with respect to th e corresponding binary ones. A synergism between V and W oxide surface species is suggested, which accounts for the high reactivity of the t ernary samples in the SCR reaction. It is suggested that the higher re ducibility 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.