The poisoning and regeneration effect of alkali metals deposed over commercial V₂O₅-WO₃/TiO₂ catalysts on SCR of NO by NH₃
2014
Gao, Fengyu | Tang, Xiaolong | Yi, Honghong | Zhao, Shunzheng | Zhang, Tongtong | Li, Dong | Ma, Ding
In this study, commercial V₂O₅-WO₃/TiO₂ catalysts were deactivated by loading with alkali metals (K and Na). These catalysts were then regenerated by washing with either deionized water or 0.5 mol/L H₂SO₄ (through the ultrasonic-assisted method). The samples used in this research were characterized by NH₃-temperature programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS). Results showed that Na₂O and K₂O doping can poison the V₂O₅-WO₃/TiO₂ catalyst and that the poisoning effect of Na₂O was stronger than that of K₂O. However, the Na₂O-loaded sample was easier to regenerate than the K₂O-loaded sample. The surfaces of catalysts can be sulfated by washing with dilute sulfuric acid because strong acid sites adhere to the catalyst surface. SO₄ ²⁻ could also promote catalyst activity. As indicated by the NH₃-TPD findings, the deposition of Na₂O and K₂O could also reduce the amount of desorbed ammonia and destabilize the acid sites, especially strong chemisorption sites. XPS results revealed that catalysts were deactivated by the decrease in the concentration of chemisorbed oxygen [the Oα/(Oα + Oᵦ) ratio]. In the Na₂O-doped catalyst, much chemisorbed oxygen was lost (from 28.8 % to 10.6 %). However, the decrease in the Oα/(Oα + Oᵦ) ratio was less significant in the K₂O-doped catalyst (from 28.8 % to 23.5 %). Nonetheless, the binding energies of O1s broadened with respect to both high and low energy. In particular, the binding energy of chemisorbed oxygen increased from 531.5 to 531.8 eV.
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