Water vapor is typically present in diesel engine exhausts, and thus the design of catalysts with high water-tolerance is highly desired. The addition of water vapor was shown to have quite different influences on the activity of Ag/Al 2 O 3 catalysts with different Ag loadings during the H 2-assisted C 3 H 6-SCR of NOx (H 2-C 3 H 6-SCR). The 2 wt% Ag/Al 2 O 3 catalyst showed the best activity for H 2-C 3 H 6-SCR, with excellent water resistance over the whole temperature range. An enhancement in NOx conversion was observed after water vapor was introduced, particularly at low temperatures. Over this catalyst, kinetic studies confirmed that H 2 O addition did not change the apparent activation energy for NOx reduction, while it increased the reaction order of C 3 H 6 from −0.62 to 0.73. This result indicated that the reaction pathway for NOx reduction was hardly changed by the introduction of water vapor, while a poisoning effect related to C 3 H 6 oxidation was decreased. In situ DRIFTS studies and DFT calculations revealed that water vapor significantly inhibits the formation of inert formate during the H 2-C 3 H 6-SCR process, and thus more sites are available for the formation of active enolic species and acetates, finally leading to increased activity for 2 wt% Ag/Al 2 O 3 in NOx reduction.

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