The influence of different magnesium (Mg) weight percentages (1, 2.5, 5, 7.5 and 10) over silver (3 wt%) impregnated alumina (SA) catalyst was investigated for the reduction of NO by C3H6. Mg doped SA catalysts were prepared by conventional impregnation method and characterized by XRD, BET-SA, ICP-MS, XPS, SEM, UV-DRS, H-2-TPR and O-2-TPD. The existence of MgO and MgAl2O4 phases on Mg doped SA catalysts were observed from XRD and XPS analyses. Existence of high percentage MgAl2O4 phase on 5% Mg doped SA catalyst (Mg (5) SA) enhances the dispersion and stabilization of silver phases (Ag2O). Mg (5) SA catalyst shows a 51% of high selectivity (NO to N-2) in presence of SO2 (80 ppm) at low temperatures (350 A degrees C) and maintained high selectivity's with a wide temperature window (350-500 A degrees C). An optimal high surface availability of Ag-0 and Ag+ species were observed from XPS analysis over Mg (5) SA catalyst. H-2-TPR analysis shows high temperature reduction peak over Mg (5) SA compared to SA catalyst. XPS analysis confirms the high percent availability of MgAl2O4 species over Mg (5) SA catalyst. DRIFTS study reveals the molecular evidences for the evolution of enolic species during NO reduction over the highly active Mg (5) SA catalyst at low temperatures. It also confirms further transformation of enolic species into -NCO species with NO + O-2 and finally into N-2 and CO2.