Exceptional Activity for NO Selective Catalytic Reduction Achieved via Cerium 4f → 5d Electron Transition

Environmentally benign cerium-based catalysts are considered promising alternatives to vanadium-based catalysts for NO selective catalytic reduction (SCR) with NH3, but insufficient low-temperature activities hamper their practical applications for NO emission control owing to ceria's intrinsic basicity and relatively large Ce4+ → Ce3+ energy barriers. Herein we solve this issue by substituting surface lattice cerium atoms with strong acidic molybdenum atoms to achieve a single-atom catalyst (Mo1©CeO2) that exhibits much higher SCR activity than pure CeO2 under identical reaction conditions. Brønsted-acid sites and Lewis-acid sites are simultaneously present on Mo1©CeO2 after the atomic Mo doping, rendering the Brønsted- ↔ Lewis-acid transformation required for efficient SCR more facile. Electronic perturbation via the d-p-d orbital interplay among the Mo–O–Ce bonds narrows the gap between the Ce's highest occupied band orbitals and the lowest unoccupied band orbitals, and induces the Ce 4f → 5d electron transition, facilitating the activation of NH3 and O2, and hence speeding up the SCR rates. This simple atomic doping strategy could simultaneously enhance acidic properties and increase the charge density of the frontier Ce 5d orbitals, which has implications for designing efficient cerium-based SCR catalysts.