Promotion effect of tungsten oxide on SCR of NO with NH3 for the V2O5-WO3/Ti0.5Sn0.5O2 catalyst: Experiments combined with DFT calculations

Binary metal oxides V2O5-WO3 supported on Ti0.5Sn0.5O2 (hereafter denoted as TS) catalysts have been characterized by XRD, LRS, TPR, NH3-TPD, in situ FT-IR and the micro-reactor test for the removal of NO by NH3. The results suggest that: (1) both vanadium oxide and tungsten oxide (loadings <= 0.5 mmol/100 m(2) TS) are highly dispersed on TS support. (2) The reduction temperature of vanadium species becomes higher due to the formation of the V-O-W bonds. (3) With the loading amounts of WO3 increasing, the amounts of the Bronsted acid sites increase, while the amounts of Lewis acid sites decrease. The strength of Bronsted acid sites is little influenced by the tungsten species which is further proved by the density functional theory (DFT) calculation results. The adsorption of NO is little changed after WO3 addition. Further increase of WO3 (loadings >= 1.0 mmol/100 m(2) TS) results in the formation of crystalline WO3 and they will cover the vanadium oxide species on the surface of the catalysts. (4) The activity of "NO + NH3 + O-2" reaction is tightly related to the amounts of the Bronsted acid sites: the higher SCR activities should be attributed to the larger amounts of Bronsted acid sites when WO3 are highly dispersed. When the crystalline WO3 form, they cover the surface of the catalysts, and lead to the decrease of the activities. (C) 2011 Elsevier B.V. All rights reserved.