Single-Atom Ce-Modified α-Fe<sub>2</sub>O<sub>3</sub> for Selective Catalytic Reduction of NO with NH<sub>3</sub>
Wei Chen, Shan Yang, Hao Liu, Fang Huang, Qinghao Shao, Lichen Liu, Jingfang Sun, Chuanzhi Sun, Dezhan Chen, Lin Dong
Abstract
A single-atom Ce-modified α-Fe2O3 catalyst (Fe0.93Ce0.07Ox 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 NOx 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 FeOx 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 FeOx 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 Fe0.93Ce0.07Ox catalyst and further facilitate the reduction of NOx by NH3. In addition, the decomposition of NH4HSO4 can occur at lower temperatures on the Fe0.93Ce0.07Ox 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.