Discerning the Role of Ag-O-Al Entities on Ag/γ-Al2O3 Surface in NOx Selective Reduction by Ethanol

Alumina-supported silver catalysts (Ag/Al2O3) derived from AlOOH, Al(OH)(3), and Al2O3 were investigated for the selective catalytic reduction of NOx by ethanol. In order to discern the role of support Al skeleton in anchoring silver species and reducing NOx, the series of alumina-supported silver catalysts calcined at different temperatures was characterized by means of in situ DRIFTS, XPS, UVvis DRS, XRD, BET, and NMR. It was found that the NOx reduction efficiency order as affected by alumina precursors could be generally described as AlOOH > Al2O3 >> Al(OH)(3), with the optimum calcination temperature of 600 degrees C. XPS and UV-vis results indicated that silver ions predominated on the Ag/Al2O3 surface. Solid state NMR suggested that the silver ions might be anchored on Al tetrahedral and octahedral sites, forming Ag-O-Al-tetra and Ag-O-A(locta) entities. With the aid of NMR and DFT calculation, A(locta) was found to be the energetically favorable site to support silver ions. However, DFT calculation indicated that the Ag-O-Al-tetra entity can significantly adsorb and activate vital -NCO species rather than the Ag-O-Al-octa entity. A strongly positive correlation between the amount of Al-tetra structures and N-2 production rate confirms the crucial role of Al-tetra in NOx reduction by ethanol.