Effect of promoters including WO_3 and BaO on the activity and durability of V_2O_5/sulfated TiO_2 catalyst for NO reduction by NH_3

摘要

The effect of tungsten and barium oxides on the activity and durability of V_2O_5/TiO_2 catalyst for NO reduction by NH_3 was examined. Tungsten enhanced the NO removal activity of V_2O_5 catalyst supported on sulfur-free TiO_2, while no effect of tungsten was observed for the V_2O_5 catalyst supported on sulfated TiO_2. The tungsten oxide promotes the formation of polymeric vanadate that is a strong active reaction site for NO reduction by NH_3. When both tungsten and sulfur simultaneously exist on the surface of V_2O_5/TiO_2, the sulfur species seems to play a more important role for NO removal activity than tungsten. The tungsten oxide on the V_2O_5/TiO_2 catalyst also enhances the activity for SO_2 oxidation by promoting the adsorption of SO_2, regardless of the presence of sulfur species on the catalyst surface. The NO removal activity of V_2O_5 catalyst supported on sulfur-free TiO_2 has been significantly reduced by barium oxide, mainly due to the formation of inactive V-O-Ba compound through the strong interaction of vanadia with barium oxide. No change of NO removal activity over V_2O_5-BaO/sulfated TiO_2, however, was examined by the addition of barium oxide, since the structure of vanadium oxide was not altered on the surface of the sulfated TiO_2. The SO_2 oxidation reaction ovre V_2O-5-BaO/TiO_2 catalysts was significantly suppressed by the addition of barium oxide to the catalyst. The barium oxide seems to reduce the redox ability of vanadium oxide on the catalyst surface as well as the adsorption capacity of SO_2. Based on the temperature programmed reduction (TPR), Ramana dn XPS observations, the surface structure of vanadium and its interaction with tungsten and barium oxides has been illustrated when sulfur exists on the surface of TiO_2.