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

The mechanism of arsenic poisoning of CeO₂-WO₃ (CW) and CeO₂-MoO₃ (CM) catalysts during the selective catalytic reduction (SCR) of NO_x 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 NO_x 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.