Structures And Electronic Properties Of Small Clusters Supported On The Doped MgO Surfaces

Magnesium oxide as a typical ionic metal oxide that the structure and properties are relatively simple is often used as catalyst supports in heterogeneous catalysis.Doping has been proved to be a common approach for tailoring the chemical and catalytic activity properties of MgO,and has important application in industry.The main objective of the present work is to deeply investigate the influences of different kinds of dopants on the preperties of the MgO surface.In this work,the stability configurations and electronic structures of W₃O₉ and Aun?n=1-4?clusters deposited on Li and Al-doped MgO?001?surfaces were investigated by using the first-principles molecular dynamic simulations combined with quantum mechanical calculations.Our calculated results show that the type of doping atoms has influence on the properties of MgO?001?surfaces.From a thermodynamical point of view,the introducing of Al dopant in MgO?001?surface is more easier than that of Li dopant.The analyses of density of states indicate that,with respect to the undoped surface,the Fermi level of Li-doped system shifts towards the higher binding energy;however the opposite movement of the Fermi level is observed when the A1 atom is introduced,which is located at the bottom of the conduction band of the undoped surface.By analyzing the most stable configurations of W₃O₉ clusters deposited on Li and Al-doped MgO?001?surfaces,when the doping is occurred on the top-layer of the MgO?001?surface,the configurations of the W₃O₉ clusters are sensitive to the type of dopant.For the electron-deficient Li doping,the cyclic conformation of W₃O₉ cluster in the gas phase is not stable and transforms into a chain-like structure.While the introduction of the A1 dopant will make the surface electron-rich,the W₃O₉ cluster tends to be adsorbed by parallel and vertical arrangements,respectively.The stabilities of two models are similar,but in the former case one terminal oxygen of the cluster becomes a capped oxygen by bonding with three W atoms.When doping at the sublayer,the W₃O₉ cluster still showes a cyclic conformation and favors a vertical deposition model.After supporting on the doped surface,W₃O₉ cluster gains electrons,however the details of the charge transfer are depent on the type of dopant.Comparison with the Li-doping surface,the Al-doping can obviously enhance the interactions between W₃O₉ and the MgO?001?surface,and more electrons are transferred from the substrate to certain W atoms,which will have significant effects on the catalytic performance of the W₃O₉ clustersExamining the configurations and electronic structures of Aun?n=1-4?clusters deposited on the Li and Al-doped MgO?001?surfaces,it can be concluded that on the Li-doped surface,the Au atom of clusters tends to be bound to the surface oxygen atom.For Au2 cluster,it adopts a configuration nearly perpendicular to the surface,and for Au3 and Au4 clusters,the triangular and distorted quadrangle configurations in the gas phase are preserved.When a surface Mg atom is replaced by A1 atom,the Au atom prefers to form bond with the surface metal atom,now Au2 cluster tends to be adsorbed parallelly,and Au3 and Au4 clusters favor the chain-like strucures after supporting.In addition,for the Al doping system,the charge transfer between cluster and substrate are remarkable,which will lead to obvious change of the surface work function.