Effects of WO(x) modification on the activity, adsorption and redox properties of CeO2 catalyst for NO(x) reduction with ammonia.

A series of WO3/CeO2 (WO(x)/CeO2) catalysts were synthesized by wet impregnation of ammonium metatungstate on a CeO2 support. The resulting solid acid catalysts were characterized by X-ray diffraction (XRD), UV-Vis spectroscopy (UV-Vis), Raman spectroscopy (Raman), in-situ Fourier transform infrared spectroscopy (in-situ FT-IR) of ammonia adsorption, NH3-TPD, H2 temperature-programmed reduction (H2-TPR), NH3/NO oxidation and activity measurements for NO(x) reduction by NH3 (NH3-SCR). The results show that polytungstate (WO(x)) species are the main species of tungsten oxide on the surface of ceria. The addition of tungsten oxide enhances the Brönsted acidity of ceria catalysts remarkably and decreases the amount of surface oxygen on ceria, with strong interaction between CeO2 and WO(x). As a result, the N2 selectivity of NH3 oxidation and NH3-SCR at high temperatures (> 300 degrees C) is enhanced. Therefore, a wide working temperature window in which NO(x) conversion exceeds 80% (NO(x) conversion > 80%) from 200 to 450 degrees C, is achieved over 10 wt.% WO(x)/CeO2 catalyst. A tentative model of the NH3-SCR reaction route on WO(x)/CeO2 catalysts is presented.