Theoretical Study Of The Geometrical And Electronic Structure Of Cu_n/TiO₂ And Bromobenzene On CuPd Alloy

Many experimental results show that the supported metal catalysts exhibit different chemical properties from the parent materials.This technology has been widely used in the field of heterogeneous catalysis and photocatalysis.Supported copper-based catalysts have attracted much attention due to the lower-cost.For example,in the anaerobic dehydrogenation of amines and alcohols,Cu/Al₂O₃ shows good catalytic activity and selectivity.For methanol synthesis,Cu/t-ZrO₂ is an excellent catalyst.For water-gas shift reaction,the catalytic activity of Cu/TiO₂?110?is the highest and the activation energy required is the lowest.Similar to gold,copper also has LSPR effect,and copper/titanium dioxide has a certain catalytic effect on the photoreduction of CO₂ and the formation of acetone.In view of the ideal catalytic activity of Cu/TiO₂ for some reactions,it is necessary to explore the internal structure and the essence of the catalyst.The stable adsorption configurations and energies of the smaller copper clusters?n=1-4?on the surface of TiO₂?110?have been reported.However,so far,the growth of larger copper clusters on the TiO₂ surface and the interaction mechanism between them are not clear.In this study,rutile TiO₂?110?,which is the most stable crystal surface of titanium dioxide,is chosen as the substrate.The growth pattern of Cu_n?n=1-14?clusters on the TiO₂?110?surface is simulated by DFT method which vdw interaction is also considered.The electronic structure as well as the essence of interaction are also explored.The results show that the copper clusters are mainly planar or quasi-planar structures when n=1-7,in which the copper atoms on the boundary are closer to the surface than those in the middle region;when n?8,the copper clusters are three-dimensional modes,but they are different from the stable configurations in the gas phase.Among all the adsorption configurations,copper clusters are mainly concentrated between two rows of two-coordinated oxygen atoms on the TiO₂ surface.With the increase of n,the absolute value of average binding energy increases gradually,which indicates that the larger size of copper clusters,the stronger the interaction between copper clusters and the surface.Bader charge analysis shows that electrons are mainly transferred from copper clusters to the surface.This may be the fact that most oxygen atoms on the surface have strong electronegativity,which easily attracts electrons and makes the copper particles charged positively as a whole.The density of states analysis?DOS?shows that the bandgap of TiO₂ decreases due to the loading of copper clusters.This means that the electron transfer between them becomes easier,so they show higher catalytic activity in some reactions under visible light irradiation.In order to investigate the catalytic reaction mechanism of CuPd alloy for halogenated hydrocarbons and the change of substrates during the reaction,bromobenzene is chosen as the adsorbate molecule,and its adsorption on the surface of CuPd alloy with different proportions?mainly pure palladium,Cu:Pd=1:3,Cu:Pd=1:1,Cu:Pd=3:1 and pure copper?is systematically calculated.The results show that after BSSE correction,the absolute values of adsorption energies of bromobenzene on these five surfaces are followed by Pd>Cu:Pd=1:3>Cu:Pd=1:1>Cu:Pd=3:1>Cu.It can be seen that the interaction between bromobenzene and pure palladium surface is the strongest,the absolute value of adsorption energy is as high as4.56 eV;the interaction between bromobenzene and pure copper is the weakest,and the absolute value of adsorption energy is only 2.05 eV;the absolute value of adsorption energy for the surface containing both metals ranges from 2.31 to 4.10 eV.In all stable adsorption configurations,the C-C bond in the bromobenzene molecule surrounding the carbon ring are parallelled to the metal surface,and all hydrogen and bromine atoms tilt upward at a certain angle.Except on the surface of pure copper,all bromine atoms are located above the palladium atom.The bond length of C-Br is longer than that of gas phase.Because there are five distinct surface,the adsorption sites of bromobenzene are also different.According to the adsorption law of the sites,the C-Br bond breakage of bromobenzene molecule on these surfaces are also simulated.The results show that the activation energy required for bond breaking on the surface of Cu:Pd=1:3 is smallest,and the barrier on the surface of Cu:Pd=1:1is largest.