Optimizing acid promoters of Ce-based NH3-SCR catalysts for reducing NOx emissions

• Published in: Catalysis today 2021-12, Vol.382, p.34-41
• Main Authors: Liu, Shuang, Yao, Pan, Lin, Qingjin, Xu, Shuhao, Pei, Mingming, Wang, Jianli, Xu, Haidi, Chen, Yaoqiang
• Format: Article
• Language: English
• Subjects: Active sites; Ce2Mo3O13; Interaction; Molybdenum; NH3-SCR; Tungsten
• ISSN: 0920-5861; 1873-4308
• DOI: 10.1016/j.cattod.2021.05.007

[Display omitted] •SCR temperature window of WO3/CeZrOx is 76 °C wider than that of MoO3/CeZrOx.•The interaction between MoO3 and CeZrOx is stronger than that of WO3 and CeZrOx.•The formation of Ce2Mo3O13 on MoO3/CeZrOx is unfavorable to NOx purification.•Ce3+ and Lewis acid sites are responsible for excellent SCR activity of WO3/CeZrOx. WO3 and MoO3 are often used as acidic promoters to modify vanadium based and non-vanadium based composite oxide catalysts, meanwhile, the NH3-SCR performance of the catalysts could be evidently improved. Generally, WO3 and MoO3 are believed to play the same role in V2O5-based and other composite oxide NH3-SCR catalysts. Interestingly, our recent work found that there are significant differences between WO3 and MoO3 in improving the NH3-SCR performance of CeZrOx. The operating temperature window of WO3/CeZrOx (222−454 °C) is 76 °C wider than that of MoO3/CeZrOx (254−410 °C) for NH3-SCR reaction. WO3/CeZrOx exhibits higher NOx removal efficiency than MoO3/CeZrOx in the whole temperature range. The similarities and differences in the effects of the acid promoters WO3 and MoO3 on the NH3-SCR performance of Ce-based catalysts are systematically investigated by Vis-Raman, XRD, XPS, NH3/O2/NOx-TPD, H2-TPR, NO/NH3-oxidation and in situ DRIFTS. Noteworthy, stronger interaction between MoO3 and CeZrOx than WO3 and CeZrOx leads to less oxygen vacancies and Lewis acid sites on the surface of MoO3/CeZrOx as well as strong oxidation property, which inhibit the NOx adsorption but contribute to the peroxidation of NH3 on MoO3/CeZrOx, reflecting its poor SCR activity. This work provides an in-depth understanding of the intrinsic effects of WO3 and MoO3 on the NH3-SCR performance of CeZrOx-based catalysts.