Chromia–Vanadia Catalysts Supported on TiO2: Effect of Composition on the Physicochemical Properties and Catalytic Performance for the Selective Catalytic Reduction of NO with NH3

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Chromia–vanadia on titania catalysts containing 8 mol% (Cr+V) were prepared and tested for the selective catalytic reduction (SCR) of NO by NH3, in excess O2, in the temperature range 250–450°C. The physicochemical properties of the prepared catalysts as well as those of the corresponding single active phase-containing samples were investigated by specific surface area and pore volume measurements, X-ray powder analysis, UV–visible diffuse reflectance spectroscopy, laser-Raman microscopy, X-ray photoelectron spectroscopy, analytical electron microscopy, and temperature-programmed reduction experiments. The best catalytic performance was achieved by the catalyst containing 2 mol% Cr and 6 mol% V (TiCr2V6), while all the binary active phase-containing catalysts proved to be more active than the corresponding single active phase-containing catalysts, at reaction temperatures higher than 350°C. The enhanced catalytic performance of the binary active phase-containing catalysts is attributed to a synergy developed between the two active phases. This synergy is maximized in the TiCr2V6sample, where a new Raman band, at 971 cm−1, has also been observed. This peak is attributed to isolated Cr6+species decorated by well-dispersed V5+species. Deposition of the chromia phase on the titania surface stabilizes the texture of the final catalysts against changes provoked by deposition of the vanadia phase.