Acidity, surface species, and catalytic activity study on V2O5-WO3/TiO2 nanotube catalysts for selective NO reduction by NH3

Abstract In this work, we report the catalytic activity of V 2 O 5 /TiO 2 , V 2 O 5 -WO 3 /TiO 2 and WO 3 /TiO 2 -nanotube model catalysts in removing NO with NH 3 via the SCR process. The catalytic activity includes the effect of SO 2 and H 2 O. We also analyze the effect of WO 3 and V 2 O 5 loading upon the surface acidity of the nanotubes, and the effect of WO 3 on the V 4+ /V 5+ ratio, and its correlation with the catalytic activity. TiO 2 -nanotubes (NT), employed as support, were prepared by hydrothermal treatment of TiO 2 with NaOH. The catalysts were characterized by X-ray diffraction, HR-TEM microscopy, N 2 physisorption, FTIR, H 2 -TPR, Raman and XPS. In general, we found that ternary catalysts (V 2 O 5 -WO 3 /NT) showed a higher NO conversion versus V 2 O 5 /NT and WO 3 /NT model catalysts. In fact, we found a high NO conversion (93%) over 3V-10W/NT catalyst at low temperature (380 °C). In the presence of SO 2 (50 ppm) and H 2 O (5 vol.%), NO conversion slightly decreases (from 93 to 80% at 380 °C). The surface acidity (Bronsted and Lewis) of the nanotubes is the main parameter improved by adding V 2 O 5 . WO 3 preferably modifies the Lewis acid sites of the nanotubes. Additionally, the structure and morphology of the nanotubes as well as the V 4+ /V 5+ ratio, which depend on the metal loading, play an important role in the removal of NO at intermediate temperatures even in the presence of SO 2 and H 2 O.