The selective catalytic reduction (SCR) of NOx by oxygenated hydrocarbons such as ethanol over Ag/Al2O3 is a promising candidate for NOx removal from diesel engine exhausts. Herein, different Al2O3 precursors were synthesized and employed to prepare Ag/Al2O3 catalysts. On the prepared catalysts, the states of silver species were carefully characterized. By combined with the activity tests, kinetic measurements and mechanism investigation, the structure-properties relationship in the SCR of NOx by ethanol (ethanol-SCR) over Ag/Al2O3 was set up. Also, the mechanism of NH3 formation and reaction pathway during the ethanol-SCR was proposed. The innovative results were obtained as follows: (a) Hydrothermal reactions were carried to synthesize boehmite nanorods and nanosheets. HRTEM images showed that the catalysts prepared from synthesized boehmite were polycrystal, with no specifically exposed crystalline planes. Thus, changing the morphology of supports has little influence on the activity and sulfur tolerance. The mesoporous Al2O3 supported Ag catalysts exhibited a relatively high surface area, improving the dispersion of silver. One-step synthesis by in situ loading of silver is more suitable for the preparation of mesoporous catalysts. (b) By simply precipitation with ethylenediamine anhydrous, nordstrandite was prepared. After Ag loading and calcination, the nordstrandite based Ag catalysts exhibited high surface area (above 300 m2/g). The catalysts with 2 wt% silver loading showed NOx conversions near to 100% within a wide temperature range of 600-750 K, while large amounts of NH3 were produced during the NOx reduction by ethanol. Combined with NH3-SCR or NH3-SCO catalysts, the selectivity to N2 enhanced significantly. (c) The production of ammonia during the ethanol-SCR is quiet common, which can be eliminated by changing the silver content on catalysts or the concentration of ethanol employed in the activity tests. During the ethanol-SCR over Ag/Al2O3, the hydrolysis of –NCO, as a key intermediate in NOx reduction, is the main source of NH3 yielding, as confirmed by DRIFTS and gaseous products analysis. Besides, DRIFTS results and activity tests revealed that NH3 reacted with enolic species to form –NCO, and then contributed to the formation of N2. (d) The results of UV-vis showed that Ag species were presented in both the oxidized state (including highly dispersed Ag+ ions (Ag+), oxidized silver clusters (Agnδ+)) and metallic silver clusters on Ag/Al2O3 (Agn0), of which the former was dominant on Ag/Al2O3 catalysts with 2-8 wt% silver content. The kinetic measurements, ICP-OES, H2-O2 titration characterizations confirmed that the Ag species in oxidized state played a key role in the reduction of NOx by ethanol. (e) In situ DRIFTS and DFT calculations showed for the first time that Ag doping promote the formation of enolic species, which prone to adsorbed on or close to silver site (RCH=CH-O-Ag, RCH=CH-O-Al-Ag). And this kind surface species are more active towards NO + O2 to form key intermediate of –NCO species, if compared to those enolic species absorbed merely on Al sites (RCH=CH-O-Al). By combining MS with DRIFTS, the important role of enolic species in the formation of N2 was confirmed.