Abatement of Nitrogen Oxides via Selective Catalytic Reduction over Ce₁-W₁ Atom-Pair Sites

Environmentally benign CeO₂-WO₃/TiO₂ catalysts are promising alternatives to commercial toxic V₂O₅-WO₃/TiO₂ for controlling NO_x emission via selective catalytic reduction (SCR), but the insufficient catalytic activity of CeO₂-WO₃/TiO₂ catalysts is one of the obstacles in their applications because of a lack of an in-depth understanding of the CeO₂-WO₃ interactions. Herein, we design a Ce₁-W₁/TiO₂ model catalyst by anchoring Ce₁-W₁ atom pairs on anatase TiO₂(001) to investigate the synergy between Ce and W in SCR. A series of characterizations combined with density functional theory calculations and in situ diffuse-reflectance infrared Fourier-transform experiments reveal that there exists a strong electronic interaction within Ce₁-W₁ atom pairs, leading to a much better SCR performance of Ce₁-W₁/TiO₂ compared with that of Ce₁/TiO₂ and W₁/TiO₂. The Ce₁-W₁ synergy not only shifts down the lowest unoccupied states of Ce₁ near the Fermi level, thus enhancing the abilities in adsorbing and oxidizing NH₃ but also makes the frontier orbital electrons of W₁ delocalized, thus accelerating the activation of O₂. The deep insight of the Ce-W synergy may assist in the design and development of efficient catalysts with an SCR activity as high as or even higher than V₂O₅-WO₃/TiO₂.