Theoretical Study On The Adsorption And Dissociation Of Small Molecules On Some Last Transition Bimetallic Surfaces

SO₂,CO and NO are one of the major air pollutants that may take a mighty toll on the environment and will all affect human health.To reducing the negative effects of these compounds,it is great importance to develop new and high efficiency metal catalysts especially bimetallic catalysts.Comparable with the single metal catalysts,the bimetallic catalysts show novel catalytic properties and selectivity due to ensemble effect,ligand effect,stress effect and other effects.In this thesis,the adsorption and decomposition of SO₂ on the Ni/Cu?100?metal surfaces have been studied by using the density functional theory.The adsorption and oxidation of CO and NO on Cu/Ru?0001?metal surfaces are also studied The calculated results showed that:?1?SO₂ is preferable to adsorb with its molecular plane parallel to the Ni?100?and Cu?100?surfaces,but adsorb perpendicular to the NiCuNi?100?and NiCuCu?100?bimetallic surfaces with its molecular plane.SO₂ bonds more strongly to the bimetallic surfaces than to the monometallic surfaces.The decompositions of SO₂ on all bimetallic surfaces are more facile than these of all monometallic surfaces.Two elementary steps are found for all bimetallic surfaces,and the breaking of the second S-O bond is the rate-determining step for the SO₂ dissociation.The calculated results showed that the energy barrier of the SO₂ decomposition on NiCuNi?lOO?surface is higher than that of on NiCuCu?100?,indicating that decomposition is preferable for the SO₂ on NiCuCu?100?surface than on NiCuNi?100?surface.?2?CO is preferentially absorbed perpendicular to the fcc site of Cu?111?and 4Cu@Ru?0001?surfaces through the lone pair of the carbon atom.For CO on xCu@Ru?0001??x=0-3?surfaces,CO is preferable to adsorb on the top site and bond with Ru atom.In addition,the adsorption energy increases with increase of Cu coverage,indicating that the introduction of Cu atom into the Ru catalyst may be increase the catalytic activity of Ru catalyst.CO bonds more strongly to 4Cu@Ru?0001?surface than to Cu?111?,but weakly than to Ru?0001?.The electrons transfer from the metal surface to the 2?*antibonding orbital of CO,leading an elongation of C-O bond and an increase in work function upon CO adsorption.For CO oxidation reaction on 4Cu@Ru?0001?surface,the calculated energy barrier is 0.96eV?3?NO is preferable to absorb perpendicular to the metal surfaces through the lone pair of the carbon atom.The adsorption interaction between NO and 3Cu@Ru?0001?bimetallic surface is the strongest for NO on all metal surface.The electrons transfer from metal surface to the NO 2?*antibonding orbital,leading that the adsorbed NO has some negative charge.The more the charge transfers,the longer the N-O bond elongates and the greater the stretch frequency of N-O bond red-shifts.NO is an even stronger n acceptor than is CO.Then,for NO and CO on the same metal surface,the interaction between NO and the surface is much stronger than that of CO.