Catalytic performance of highly dispersed WO 3 loaded on CeO 2 in the selective catalytic reduction of NO by NH 3

Abstract The influence of tungsten trioxide (WO 3 ) loading on the selective catalytic reduction (SCR) of nitric oxide (NO) by ammonia (NH 3 ) over WO 3 /cerium dioxide (CeO 2 ) was investigated. The NO conversion first rose and then declined with increasing WO 3 loading. It was found that the crystalline WO 3 in the 1.6WO 3 /CeO 2 sample could be removed in 25 wt% ammonium hydroxide at 70 °C, which improved the catalytic activity of the sample. The obtained samples were characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, hydrogen (H 2 ) temperature programmed reduction, NH 3 temperature programmed desorption, and in situ diffuse reflectance infrared Fourier transform spectroscopy. The results revealed that the dispersed WO 3 promoted the catalytic activity of WO 3 /CeO 2 while the crystalline WO 3 inhibited catalytic activity. The oxygen activation of CeO 2 was inhibited by the coverage of WO 3 , which weakened NO oxidation and adsorption of nitrate species over WO 3 /CeO 2 . In addition, the NH 3 adsorption performance on CeO 2 was improved by modification with WO 3 . NH 3 was the most stable adsorbed species under NH 3 SCR reaction conditions. In situ DRIFT spectra suggested that the NH 3 SCR reaction proceeded via the Eley-Rideal mechanism over WO 3 /CeO 2 . Thus, when the loading of WO 3 was close to the dispersion capacity, the effects of NH 3 adsorption and activation were maximized to promote the reaction via the Eley-Rideal route.