Synthesis of W-modified CeO2/ZrO2 catalysts for selective catalytic reduction of NO with NH3

Chenglong Li; Zhitao Han; Yuqing Hu; Tingjun Liu; Xinxiang Pan

doi:10.1039/d2ra04862k

Synthesis of W-modified CeO₂/ZrO₂ catalysts for selective catalytic reduction of NO with NH₃

RSC Adv. 2022 Sep 27;12(42):27309-27320. doi: 10.1039/d2ra04862k. eCollection 2022 Sep 22.

Authors

Chenglong Li¹, Zhitao Han¹, Yuqing Hu¹, Tingjun Liu¹, Xinxiang Pan^{1

2}

Affiliations

¹ Marine Engineering College, Dalian Maritime University No.1, Linghai Road Dalian 116026 China hanzt@dlmu.edu.cn.
² School of Electronic and Information Technology, Guangdong Ocean University Zhanjiang 524088 China.

Abstract

In this paper, a series of tungsten-zirconium mixed binary oxides (denoted as W _m ZrO _x ) were synthesized via co-precipitation as supports to prepare Ce_0.4/W _m ZrO _x catalysts through an impregnation method. The promoting effect of W doping in ZrO₂ on selective catalytic reduction (SCR) performance of Ce_0.4/ZrO₂ catalysts was investigated. The results demonstrated that addition of W in ZrO₂ could remarkably enhance the catalytic performance of Ce_0.4/ZrO₂ catalysts in a broad temperature range. Especially when the W/Zr molar ratio was 0.1, the Ce_0.4/W_0.1ZrO _x catalyst exhibited the widest active temperature window of 226-446 °C (NO _x conversion rate > 80%) and its N₂ selectivity was almost 100% in the temperature of 150-450 °C. Moreover, the Ce_0.4/W_0.1ZrO _x catalyst also exhibited good SO₂ tolerance, which could maintain more than 94% of NO _x conversion efficiency after being exposed to a 100 ppm SO₂ atmosphere for 18 h. Various characterization results manifested that a proper amount of W doping in ZrO₂ was not only beneficial to enlarge the specific surface area of the catalyst, but also inhibited the growth of fluorite structure CeO₂, which were in favor of CeO₂ dispersion on the support. The presence of W was conducive to the growth of a stable tetragonal phase crystal of ZrO₂ support, and a part of W and Zr combined to form W-Zr-O _x solid super acid. Both of them resulted in abundant Lewis acid sites and Brønsted acid sites, enhancing the total surface acidity, thus significantly improving NH₃ species adsorption on the surface of the Ce_0.4/W_0.1ZrO _x catalyst. Furthermore, the promoting effect of adding W on SCR performance was also related to the improved redox capability, higher Ce³⁺/(Ce³⁺ + Ce⁴⁺) ratio and abundant surface chemisorbed oxygen species. The in situ DRIFTS results indicated that nitrate species adsorbed on the surface of the Ce_0.4/W_0.1ZrO _x catalyst could react with NH₃ due to the activation of W. Therefore, the reaction pathway over the Ce_0.4/W_0.1ZrO _x catalyst followed both Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanisms at 250 °C.