Synergistic effect between ceria and tungsten oxide on WO3–CeO2–TiO2 catalysts for NH3-SCR reaction

WO 3 –CeO 2 –TiO 2 catalysts for NO (nitrogen monoxide) reduction by ammonia were prepared by a sol–gel method. The catalysts were characterized by BET, XRD, Raman, NH 3 /NO adsorption and H 2 -TPR to investigate the relationships among the catalyst composition, structure, redox property, acidity and deNO x activity. WO 3 –CeO 2 –TiO 2 catalysts show a high activity in a broad temperature range of 200–480   °C. The low-temperature activity of catalysts is sensitive to the catalyst composition especially under low-O 2 -content atmospheres. It may be related to the synergistic effect between CeO x and WO x in the catalysts. On one hand, the interaction between ceria and tungsten oxide promotes the activation of gaseous oxygen to compensate the lattice oxygen consumed in NH 3 -SCR (selective catalytic reduction) reaction at low temperatures. Meanwhile, the Brønsted acid sites mainly arise from tungsten oxides, Lewis acid sites mainly arise from ceria. Both of the Brønsted and Lewis acid sites facilitate the adsorption of NH 3 on catalysts and improve the stability of the adsorbed ammonia species, which are beneficial to the NH 3 -SCR reaction.