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Significant differences of NH3-SCR performances between monoclinic and hexagonal WO3 on Ce-based catalysts
Environmental Science: Nano  (IF8.131),  Pub Date : 2021-08-10, DOI: 10.1039/d1en00519g
Shuang Liu, Pan Yao, Ming-Ming Pei, Qing-Jin Lin, Shu-Hao Xu, Jian-Li Wang, Hai-Di Xu, Yao-Qiang Chen

WO3 has different crystalline structures, including monoclinic and hexagonal phases. Monoclinic WO3 (W-m) is the most common crystal phase in NH3-SCR catalysts. Hexagonal WO3 (W-h) with empty hexagonal and trigonal tunnel structures exhibits excellent acidity and reducibility and can provide abundant catalytically active sites, but it is hardly applied in the NH3-SCR reaction. Herein, the effects of different WO3 phases on the NH3-SCR performance of Ce-based catalysts are systematically investigated. The SCR activity of CeO2 is both evidently improved by the addition of W-h and W-m. It is noteworthy that CeO2–WO3-hexagonal (Ce–W-h) exhibits a more excellent NOx removal efficiency than CeO2–WO3-monoclinic (Ce–W-m) in the whole temperature window tested, and T50 and T90 of Ce–W-h are 51 and 111 °C lower than those of Ce–W-m, respectively. Importantly, compared with that of W-m, the special open structure of W-h not only facilitates NH3 adsorption and the diffusion of oxygen to improve the acidity and reducibility of the catalyst, but also is favorable for electron transfer between W-h and Ce to boost the interaction between W-h and Ce. Besides, the active plane (001) on W-h/Ce–W-h can provide abundant unsaturated W6+ and Brønsted acid sites. Accordingly, the Ce–W-h catalyst displays a more impressive NH3-SCR performance than Ce–W-m. W-h is a better choice to modify CeO2 to improve its SCR performance than W-m. This work provides a profound understanding of the intrinsic effect of the crystal phases of WO3 on NH3-SCR performance.