Theoretical Study On The Adsorption And Selective Reaction Mechanism Of Organic Molecules On Metal Surfaces

The surface and interface of metal materials are rich in physical and chemical charac-teristics,showing great potential applications in energy storage and conversion,catalysis,scensing,nano devices and other fields.However,revealing the physical essence of ex-perimental phenomena in metal surface diversity and its wide application in the new generation of high-performance components is still a great challenge in the current scien-tific research.There is an interface between the metal surface and the organic molecules,which plays a decisive role in the properties of electricity,optics and transport.Therefore,the accurate prediction of the microstructure at the interface is an important prerequisite for the development of special metal materials,the realization of functional design and the regulation of reaction.The bonding of th e interface comes from the subtle interaction,such as covalent bond,ionic bond,Pauli repulsion,van der Waals force and hydrogen bonding.There-fore,accurately predicting and describing the thermodynamic and kinetic properties of interface materials is still very difficult in theory.Density functional theory?DFT?is the only feasible calculation method to research the electronic structure of complex interface systems.However,it is known that the standard DFT functional cannot capture the screening effect of metals and the long-range van der Waals?vdW?interactions.This may lead to serious errors in the prediction of the atomic configuration,electronic struc-ture,stability and functional properties of adsorption reaction systems.Therefore,a new theoretical method is needed to deal with the interaction at the interface.Recently theoretical studies show that most methods dealing with vdW forces often neglect the important contributions of dielectric screening within the metal surface and the many-body dispersion effect?MBD?to the interface system.It has been proved that MBD method is applied well in the close-packed metal surface adsorption system.However,vacancies,kinks,and steps are inevitable in actual devices.The contribution of MBD effects to the open surface or defective surface?such as stepped surfaces?has not been systematically studied.In addition to MBD effects,the self-consistent?SC?vdW forces also has a significant influence on the electronic properties of the interface,such as the work function.Based on these correct structures obtained by these advanced vdW methods,choosing different metal surfaces,step densities,adsorption molecules and molecule coverage,to realize functional design and selective reaction control of adsorption materials is an urgent need at present.In this dissertation,we use vdW included first-principle calculations,in combination with metal screening effects and MBD effects,systematically studied the adsorption and catalytic properties between different metal surfaces?Cu,Ag,Au,Pd,Pt,Rh and Ir?and a series of organic molecules?benzene,isophorone and acrolein?.Our study illustrates the relationship between many-body contributions and the planar atomic density of metals,discovers the law via molecular adsorption and steps tuning the work functions of metal surfaces,proposes the "inner orbital mechanism",reveals the leading role of vdW forces on the weak adsorption of the surface reaction system,and provides a new idea for further research and design the hydrogenation at the C?O bond of unsaturated hydrocarbons.The major conclusions can be summarized as follows:?1?We use PBE+vdW^surf and PBE+MBD methods to systematically study benzene,naphthalene and anthracene on the low-index coinage metal surfaces.We demonstrate that the many-body contributions are sensitive to the planar atomic density of FCC metals,and follow the sequence of?111?>?100?>?110?.The delicate balance between Pauli repulsion and vdW forces leads to the identical binding energy for benzene on Ag?111?and on Au?111?,which goes against the classic d-band center theory that works well for small molecules on metals.?2?We perform DFT calculations in combination with metal screening effects and SC vdW effects,to systematically study the interactions of benzene with a variety of stepped surfaces.Our calculations show that work functions can be tailored by the surface coverage and step density of metal surfaces.The higher the step density,the larger the reduction of the work function.We further examine the effects of vdW interactions on the work function and find the importance of long-range vdW effects in properties beyond the electronic ground state.As a result,the Ag?211?stepped surface with the highest step density would be the most promising candidate to design electronic devices,due to its lowest work function upon the adsorption of benzene.?3?We systematically study 7 molecule/surface combina,tions to show that chemose-lectivity on metal surfaces can be mostly determined by the inner-lying molecular orbitals.For isophorone,these 7 metals can be divided into two types of selective hydrogenation reaction path:one is the hydrogenation of C=C bond to form unsaturated ketone on Pd?111?,Pt?111?,Rh?111?and Ir?111?surface with high activity;the other one is the hydrogenation of C=O bond to form unsaturated alcohols on Cu?111?,Ag?111l?and Au?111?surface with low reactivity.The extent of broadening of inner molecular orbitals might be used as a guiding principle to predict the chemoselectivity for a wide class of catalytic reactions at metal surfaces.?4?The adsorption and catalytic properties of acrolein on transition metal surfaces with different coverage are studied by PBE+vdW^surf method.We discuss the relation-ship between functional,molecular coverage,structure and reaction selectivity.We also demonstrate the universality of the inner orbital broadening mechanism.The results show that vdW forces lead to more possibility in reaction,and desorption is the key step to inhibit the hydrogenation on the C?O bond.Meanwhile,the inner orbital mechanism is suitable for describing the selective hydrogenation of a series of unsaturated aldehydes?ketones?on metal surfaces,as well as higher surface coverage and hydrogen-precovered surface.