Atom Pairing Enhances Sulfur Resistance in Low-Temperature SCR via Upshifting the Lowest Unoccupied States of Cerium.

Environmentally benign cerium-based catalysts are promising alternatives to toxic vanadium-based catalysts for controlling NO x emissions via selective catalytic reduction (SCR), but conventional cerium-based catalysts unavoidably suffer from SO 2 poisoning in low-temperature SCR. We develop a strongly sulfur-resistant Ce 1+1 /TiO 2 catalyst by spatially confining Ce atom pairs to different anchoring sites of anatase TiO 2 (001) surfaces. Experimental results combined with theoretical calculations demonstrate that strong electronic interactions between the paired Ce atoms upshift the lowest unoccupied states to an energy level higher than the highest occupied molecular orbital (HOMO) of SO 2 so as to be catalytically inert in SO 2 oxidation but slightly lower than HOMO of NH 3 so that Ce 1+1 /TiO 2 has desired ability toward NH 3 activation required for SCR. Hence, Ce 1+1 /TiO 2 shows higher SCR activity and excellent stability in the presence of SO 2 at low temperatures with respect to supported single Ce atoms. This work provides a general strategy to develop sulfur-resistant catalysts by tuning the electronic states of active sites for low-temperature SCR, which has implications for practical applications with energy-saving requirements.