Selective catalytic reduction of nitrogen oxide by ammonia over V₂O₅/TiO₂ containing WO₃ and MoO₃ catalysts

Abstract

This work studies the selective catalytic reduction (SCR) of nitrogen oxide by ammonia over V₂O₅/TiO₂ containing WO₃ and MoO₃ catalysts. The support, titanium dioxide is prepared by a sol-gel method. The vanadium, tungsten and molybdenum are loaded to the prepared TiO₂ by incipient wetness method. Various techniques including ICP-OES, XRD, nitrogen adsorption, NH₃-TPD and FT-IR are employed to characterize the catalysts. The catalytic activity testing is carried out in a temperature range 100-450℃. The results indicate that 3VxWyMo catalyst system shows good catalytic performances at low to intermediate temperature. The sequence of loading metal oxides (V, W and Mo) and calcinations influences the SCR activity significantly. An optimal catalyst preparation is loading V, calcination at 500℃ for 2 hr, loading Mo, calcinations at 500℃ for 2 hr and finally loading W, calcinations at 500℃ for 2 hr. Moreover, the research also found that the decreasing of the contents of W and Mo down from 7 and 10 wt.% respectively does not improve the SCR activity. The suitable compositions of WO₃ and MoO₃ over V₂O₅/TiO₂ catalyst are 7 and 10 wt.% respectively. The presence of H₂O and SO₂ can reduce the oxidation of NH₃ to NO at high temperature. It is believed that H₂O and SO₂ can competitively adsorb with NH₃ on the site which can oxidize NH₃ to NO. The blocking of this site results in lower NH₃ oxidation.