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

In this work, we report the catalytic activity of V2O5/TiO2, V2O5-WO3/TiO2 and WO3/TiO2- nanotube model catalysts in removing NO with NH3 via the SCR process. The catalytic activity includes the effect of SO2 and H2O. We also analyze the effect of WO3 and V2O5 loading upon the surface acidity of the nanotubes, and the effect of WO3 on the V4+/V5+ ratio, and its correlation with the catalytic activity. TiO2- nanotubes ( NT), employed as support, were prepared by hydrothermal treatment of TiO2 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 ( V2O5- WO3/NT) showed a higher NO conversion versus V2O5/NT and WO3/NT model catalysts. In fact, we found a high NO conversion ( 93%) over 3V- 10W/ NT catalyst at low temperature ( 380 degrees C). In the presence of SO2 ( 50 ppm) and H2O ( 5 vol.%), NO conversion slightly decreases ( from 93 to 80% at 380 degrees C). The surface acidity ( Bronsted and Lewis) of the nanotubes is the main parameter improved by adding V2O5. WO3 preferably modifies the Lewis acid sites of the nanotubes. Additionally, the structure and morphology of the nanotubes as well as the V4+/V5+ ratio, which depend on the metal loading, play an important role in the removal of NO at intermediate temperatures even in the presence of SO2 and H2O. (C) 2016 Elsevier Ltd. All rights reserved.