Effect of WO₃ content on the catalytic activity of CeO₂-ZrO₂-WO₃ for selective catalytic reduction of NO with NH₃

A series of CeO₂-ZrO₂-WO₃ catalysts (CZW) was prepared by the hydrothermal method. The effect of WO₃ content on their catalytic properties for selective reduction of NO_<em>x with NH₃ was investigated. The catalysts were characterized by X-ray diffraction, N₂ sorption, H₂ temperature-programmed reduction, NH₃ temperature-programmed desorption and NO temperature-programmed desorption techniques. It was shown that WO₃ existed as amorphous species in the CZW. Introduction of WO₃ in the CZW dramatically enhanced its surface acidity and gave rise to strongly adsorbed NO species, consequently increasing the catalytic activity. In addition, appropriate amounts of WO₃ also increased the surface area and improved the reduction behavior of the catalyst. Compared to the CeO₂-ZrO₂, the CZW with 20% WO₃ not only exhibited high resistivity to SO₂, but also had a wider reaction temperature window. It showed a NO_x conversion of> 90% at the space velocity of 60 000 h^-1 in the temperature range of 200~463 ℃.