Insight into the Promotion Effect of Trace Pd Doping on the Catalytic Performance of Ag/Al2O3 for C3H6-SCR of NOx

The mechanistic cause of the enhancement of the C₃H₆-SCR activity of Ag/Al₂O₃ by trace Pd doping and the corresponding structure-property relationship were investigated. Pd doping enhanced the water resistance of Ag/Al₂O₃ for C₃H₆-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/Al₂O₃ was suppressed during the partial oxidation of C₃H₆, 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.