A series of silver-doped cerium zirconium oxide(Ag-CexZr) samples was synthesized successfully for selective catalytic reduction of nitric oxide(NO) with hydrogen and propene(H2/C3H6-SCR) under excess oxygen condition.The catalytic activity test proved that Ag-Ce0.4Zr exhibited the best C3H6-SCR activity.Hydrogen(H2) significantly enhanced NO conversion and widened the temperature window.Multi-technology characterizations were conducted to ascertain the properties of fabricated catalysts including X-ray diffraction(XRD),Fourier transform infrared spectrometry(FTIR),scanning electron microscopy(SEM) and H2 temperature programmed reduction (H2-TPR).In situ FTIR results demonstrated that various types of nitrates and chelating nitrite were generated on Ag-CexZr after introduction of NO.Besides,adding H2 could increase the concentration of bidentate nitrate and chelated bidentate nitrate dramatically,especially for Ag-Ce0.4Zr catalyst.Transient reaction between pre-adsorbing NO and C3H6/C3H6+H2 illuminated that the most active intermediate was chelating nitrite,which was promoted significantly by H2 participation.Furthermore,adding H2 improved the formation of organo-nitro(R-NO2),which was the key intermediate in C3H6-SCR.The reaction mechanism over Ag-CexZr catalysts was proposed at 200 ℃ as follows: nitric oxide(NO)+propene(C3H6)+hydrogen(H2)+oxygen(O2)→chelating nitrite(NO2-)+acrylate-type species(CxHyOz)→ organo-nitro(R-NO2)→isocyanate(-NCO)+cyanide(-CN)→ nitrogen(N2).