Elucidating the facet-dependent reactivity of CrMn catalyst for selective catalytic reduction of NOx with NH3

Ninghan Wei; Cheng Zhao; Xiaomei Hu; Zhangfa Tong; Junge Yun; Xueying Jiang; Chengxian Liu; Keju Wang; Yun Zou; Zhihang Chen

doi:10.1016/j.scitotenv.2022.158881

Elucidating the facet-dependent reactivity of CrMn catalyst for selective catalytic reduction of NO_x with NH₃

Sci Total Environ. 2023 Jan 10:855:158881. doi: 10.1016/j.scitotenv.2022.158881. Epub 2022 Sep 19.

Authors

Ninghan Wei¹, Cheng Zhao², Xiaomei Hu², Zhangfa Tong¹, Junge Yun³, Xueying Jiang¹, Chengxian Liu¹, Keju Wang¹, Yun Zou⁴, Zhihang Chen⁵

Affiliations

¹ School of Chemistry and Chemical Engineering, Guangxi University, Nanning 530004, PR China.
² Guangdong Key Lab of Water & Air Pollution Control, Guangdong Province Engineering Laboratory for Air Pollution Control, South China Institute of Environmental Sciences, Ministry of Ecology and Environment, Guangzhou 510655, PR China.
³ College of Environment and Resources, Xiangtan University, Xiangtan, 411105, PR China.
⁴ School of Chemistry and Chemical Engineering, Guangxi University, Nanning 530004, PR China. Electronic address: zouyun@gxu.edu.cn.
⁵ Guangdong Key Lab of Water & Air Pollution Control, Guangdong Province Engineering Laboratory for Air Pollution Control, South China Institute of Environmental Sciences, Ministry of Ecology and Environment, Guangzhou 510655, PR China; College of Environment and Resources, Xiangtan University, Xiangtan, 411105, PR China. Electronic address: chenzhihang@scies.org.

PMID: 36411606
DOI: 10.1016/j.scitotenv.2022.158881

Abstract

The facet-dependent reactivity of CrMn catalysts was still unclear, hindering the further enhancement of their low-temperature SCR performance. Herein, the facet-dependent reactivity of CrMn_1.5O₄ catalyst for NH₃-SCR of NO_x was innovatively illustrated by numerous characterizations and density functional theory (DFT) calculations. Exposed (100) facet of CrMn_1.5O₄ catalyst exhibited best low-temperature SCR activity with ≥90 % NO conversion within 148-296 °C and 2.86 × 10^-3 mol/(g·s) reaction rate within 160-240 °C. The characterizations revealed that (100) facet could induce the increase of BET specific area, electron transfer, concentration of Mn⁴⁺ and O_α, surface acidity, redox ability, NH₃ and NO_x adsorption/activation capacity. Subsequently, DFT calculations demonstrated that (100) facet exhibited the strongest affinity for NH₃ and NO due to its unique 3O_3c-Mn_5c-2O_4c bond and abundant charges transfer near the active adsorption sites, and Brønsted acid and oxygen vacancies were most easily formed on (100) facet. Furthermore, H₂O formation as the rate determining step easily occurred on (100) facet. Eventually, we successfully improved the low-temperature SCR activity of CrMn_1.5O₄ catalyst by further tailoring highly active (100) facet from 0.754 to 0.865. This work provides the deeper understanding of facet-dependent reactivity and a good strategy to improve the catalytic activity of the catalysts.

Keywords: CrMn(1.5)O(4); DFT calculations; Facet-dependent reactivity; Low-temperature; NH(3)-SCR.

MeSH terms

Adsorption
Ammonia* / chemistry
Catalysis
Oxidation-Reduction
Temperature

Substances

Ammonia