Comparison of the Structures and Mechanism of Arsenic Deactivation of CeO2–MoO3 and CeO2–WO3 SCR Catalysts

Abstract

The mechanism of arsenic poisoning of CeO2–WO3 (CW) and CeO2–MoO3 (CM) catalysts during the selective catalytic reduction (SCR) of NOx with NH3 was investigated. It was found that the ratio of activity loss of the CW catalyst decreases as the temperature increases, while the opposite tendency was observed for the CM catalyst. The fresh and poisoned catalysts were characterized using X-ray diffraction (XRD) temperature-programmed reduction with H2 (H2-TPR), X-ray photoelectron spectra (XPS), NH3-temperature-programmed desorption (NH3-TPD), in situ DRIFTS, and in situ Raman spectroscopy. The results indicate that arsenic oxide primarily destroys the structure of the surface CeOx species in the CM catalyst but prefers to interact with WO3 in the CW catalyst. Additionally, the BET surface area, the number and stability of Lewis acid sites, and the NOx adsorption for these two types of catalysts clearly decrease after deactivation. According to the DRIFTS and Raman investigations, at low temperatures, the greater number of sites with adsorbed NH3 in the poisoned CM catalyst leads to less loss of activity than the poisoned CW catalyst. However, at high temperatures, the greater number of Lewis acid sites remaining in the poisoned CW catalyst may play an important role in maintaining the activity of this catalyst.