Single-Atom Ce-Modified α-Fe 2 O 3 for Selective Catalytic Reduction of NO with NH 3 .

A single-atom Ce-modified α-Fe 2 O 3 catalyst (Fe 0.93 Ce 0.07 O 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 NH 3 (NH 3 -SCR) over a wide operating temperature window. Remarkably, it maintained ∼93% NO conversion efficiency for 168 h in the presence of 200 ppm SO 2 and 5 vol % H 2 O 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 CeO 2 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-Fe 2 O 3 catalyst. The Fe-O-Ce sites can promote the oxidation of NO to NO 2 on the Fe 0.93 Ce 0.07 O x catalyst and further facilitate the reduction of NO x by NH 3 . In addition, the decomposition of NH 4 HSO 4 can occur at lower temperatures on the Fe 0.93 Ce 0.07 O x catalyst containing atomically dispersed Ce species than on the α-Fe 2 O 3 reference catalyst, resulting in the good SO 2 /H 2 O resistance ability in the NH 3 -SCR reaction.