Single-Atom Ce-Modified α-Fe2O3 for Selective Catalytic Reduction of NO with NH3

Wei Chen; Shan Yang; Hao Liu; Fang Huang; Qinghao Shao; Lichen Liu; Jingfang Sun; Chuanzhi Sun; Dezhan Chen; Lin Dong

doi:10.1021/acs.est.2c02916

Single-Atom Ce-Modified α-Fe₂O₃ for Selective Catalytic Reduction of NO with NH₃

Environ Sci Technol. 2022 Jul 19;56(14):10442-10453. doi: 10.1021/acs.est.2c02916. Epub 2022 Jun 24.

Authors

Wei Chen¹, Shan Yang¹, Hao Liu¹, Fang Huang¹, Qinghao Shao¹, Lichen Liu², Jingfang Sun³, Chuanzhi Sun¹, Dezhan Chen¹, Lin Dong³

Affiliations

¹ Shandong Provincial Key Laboratory of Clean Production of Fine Chemicals, College of Chemistry, Chemical Engineering and Materials Science, Institute of Materials and Clean Energy, Shandong Normal University, Jinan 250014, P. R. China.
² Department of Chemistry, Tsinghua University, Beijing 100084, P. R. China.
³ Jiangsu Key Laboratory of Vehicle Emissions Control, School of the Environment, Nanjing University, Nanjing 210093, P. R. China.

PMID: 35749227
DOI: 10.1021/acs.est.2c02916

Abstract

A single-atom Ce-modified α-Fe₂O₃ catalyst (Fe_0.93Ce_0.07O_x catalyst with 7% atomic percentage of Ce) was synthesized by a citric acid-assisted sol-gel method, which exhibited excellent performance for selective catalytic reduction of NO_x with NH₃ (NH₃-SCR) over a wide operating temperature window. Remarkably, it maintained ∼93% NO conversion efficiency for 168 h in the presence of 200 ppm SO₂ and 5 vol % H₂O at 250 °C. The structural characterizations suggested that the introduction of Ce leads to the generation of local Fe-O-Ce sites in the FeO_x matrix. Furthermore, it is critical to maintain the atomic dispersion of the Ce species to maximize the amounts of Fe-O-Ce sites in the Ce-doped FeO_x catalyst. The formation of CeO₂ nanoparticles due to a high doping amount of Ce species leads to a decline in catalytic performance, indicating a size-dependent catalytic behavior. Density functional theory (DFT) calculation results indicate that the formation of oxygen vacancies in the Fe-O-Ce sites is more favorable than that in the Fe-O-Fe sites in the Ce-free α-Fe₂O₃ catalyst. The Fe-O-Ce sites can promote the oxidation of NO to NO₂ on the Fe_0.93Ce_0.07O_x catalyst and further facilitate the reduction of NO_x by NH₃. In addition, the decomposition of NH₄HSO₄ can occur at lower temperatures on the Fe_0.93Ce_0.07O_x catalyst containing atomically dispersed Ce species than on the α-Fe₂O₃ reference catalyst, resulting in the good SO₂/H₂O resistance ability in the NH₃-SCR reaction.

Keywords: DFT calculations; Fe2O3; NH3-SCR; SO2/H2O tolerance; atomically dispersed Ce.