The influence of tungsten and vanadium oxides on the microstructure, phase formation and De-NOx activity of selective catalytic reduction (SCR) catalysts has been investigated. Binary (V2O5/TiO2 and WO3/TiO2) and ternary (V2O5-WO3/TiO2) samples with compositions similar to those of commercial SCR catalysts were examined in terms of structural analyses and the reduction of NOx to N-2 in the presence of NH3. The TiO2 supported catalysts with different W- and V-loadings (WO3: 10 Wt%, V2O5 <10 wt%), heat-treated in the temperature range of 450 degrees C to 650 degrees C, have been characterized. The addition of W to TiO2 led to lowering the transition temperature of anatase-to-rutile. Upon the phase transition, WO3 phase segregation was observed. The W-loading in the TiO2 support did not influence the crystallite dimensions and surface area. In the case of the V-loading, the transition temperature was significantly reduced along with an abruptly decreased surface area due to the crystallite growth with increasing V-content. Ternary V2O5-WO3/TiO2 catalysts exhibited higher De-NOx efficiency than binary V2O5/TiO2 and WO3/TiO2 samples with the same amount of loading. In V2O5(3 Wt%)-WO3(10 Wt%)TiO2 catalysts, the highest De-NOx activity was achieved in a wide temperature range. A catalyst heat-treatment at 650 degrees C showed a relatively high efficiency and wider temperature range, maintaining peak activity in comparison with the catalysts prepared at 450 degrees C.

Keywords: selective catalytic reduction (SCR); V2O5-WO3/TiO2; NOx conversion; anatase TiO2