Adsorption states of typical intermediates on Ag/Al2O3 catalyst employed in the selective catalytic reduction of NOx by ethanol

摘要

The adsorption of ethanol and important intermediates onto Ag/Al2O3 catalyst employed in the selective catalytic reduction of NO by ethanol was simulated by density functional theory. Considering the interaction between Ag metal and Al2O3 support, typical Ag-O-Al entities, i.e., Ag-O-Al-tetra and Ag-O-Al-octa (tetra = tetrahedral and octa = octahedral refer to the coordination sites of Al), were selected as potential adsorption sites on the surface of the catalyst. Ethanol, and enolic and isocyanate species were preferentially adsorbed and activated by Ag-O-Al-tetra entities rather than by Ag-O-Al-octa entities. The strong Lewis acidity of Al-tetra in the Ag-O-Al-tetra entity was very important, enabling the entity to accept an electron via forward donation from either the C-O sigma bond in ethanol or the N-C sigma bond in the -NCO species. Moreover, the hybridization of the Ag and Al orbitals was critical for electron back donation from the Ag-O-Al-tetra entity to the C-C pi bond in the enolic species or N-C pi bond in the -NCO species. The significant activation of the N-C bond in -NCO on the Ag-O-Al-tetra sites facilitated cleavage of -NCO to form N-2. Thus, we can conclude that the acidity of the Al site and the interaction between Ag and Al play key roles in the selective catalytic reduction of NO by ethanol over Ag/Al2O3. (C) 2015, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.