Significant differences of NH3-SCR performances between monoclinic and hexagonal WO3 on Ce-based catalysts,Environmental Science: Nano

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Significant differences of NH3-SCR performances between monoclinic and hexagonal WO3 on Ce-based catalysts
Environmental Science: Nano ( IF 5.8 ) Pub Date : 2021-08-10 , DOI: 10.1039/d1en00519g
Shuang Liu ₁ , Pan Yao ₁ , Ming-Ming Pei ₂ , Qing-Jin Lin ₃ , Shu-Hao Xu ₂ , Jian-Li Wang _{2,

4} , Hai-Di Xu _{1,

2,

4} , Yao-Qiang Chen _{1,

2,

4}

Affiliation

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 NO_x 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.

中文翻译：

单斜和六方WO3在Ce基催化剂上NH3-SCR性能的显着差异

WO ₃具有不同的晶体结构，包括单斜相和六方相。单斜晶WO ₃ (Wm) 是NH ₃ -SCR 催化剂中最常见的晶相。具有空六方和三方隧道结构的六方WO ₃ (Wh)表现出优异的酸性和还原性，可以提供丰富的催化活性位点，但在NH ₃ -SCR反应中几乎没有应用。在此，系统研究了不同WO ₃相对Ce 基催化剂NH ₃ -SCR 性能的影响。通过添加Wh和Wm ，CeO ₂的SCR活性均明显提高。值得注意的是，CeO ₂–WO _{3 -}六方（Ce-Wh）在整个测试温度窗口中表现出比CeO ₂ -WO _{3 -单}斜（Ce-Wm）更优异的NO _x去除效率，并且Ce-Wh的T ₅₀和T ₉₀为51和 111 °C 分别比 Ce-Wm 低。重要的是，与Wm相比，Wh的特殊开放结构不仅有利于NH ₃吸附和氧的扩散，提高催化剂的酸性和还原性，而且有利于Wh和Ce之间的电子转移，促进相互作用Wh 和 Ce 之间。此外，Wh/Ce–Wh 上的活性面 (001) 可以提供丰富的不饱和 W ⁶⁺和 Brønsted 酸位点。因此，Ce-Wh 催化剂显示出比 Ce-Wm更令人印象深刻的 NH ₃ -SCR 性能。Wh 是改性 CeO ₂以提高其 SCR 性能的更好选择，而不是 Wm。这项工作提供了对WO ₃晶相对NH ₃ -SCR性能的内在影响的深刻理解。

更新日期：2021-09-01

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