Insight into the Promotion Effect of Trace Pd Doping on the Catalytic Performance of Ag/Al 2 O 3 for C 3 H 6 -SCR of NO x .

The mechanistic cause of the enhancement of the C 3 H 6 -SCR activity of Ag/Al 2 O 3 by trace Pd doping and the corresponding structure-property relationship were investigated. Pd doping enhanced the water resistance of Ag/Al 2 O 3 for C 3 H 6 -SCR by changing the reaction pathway. Under wet conditions, a series of in situ DRIFT studies indicated that the production of an active acetate intermediate on Ag/Al 2 O 3 was suppressed during the partial oxidation of C 3 H 6 , while trace Pd doping promoted the formation of another active intermediate, an enolic species. Furthermore, a pathway for the formation of enolic species by the reaction of acrylate with hydroxyl species was proposed. DFT calculations revealed that the surface of Ag clusters was easily covered by hydroxyl in the presence of water vapor, which could inhibit the formation of acetates. Doping with Pd facilitated the activation of acrylate which might further react with hydroxyl species to form enolic species. These findings can be helpful for the future design of efficient HC-SCR catalysts.