Reaction Mechanism Based On Surface Reconstruction Of Cu-based Catalyst

Catalyst surface reconstruction can occur in the process of catalyst preparation,activation and reaction.The structure and properties of the reconstructed catalyst may show great difference from the original catalyst.Therefore,exploring the catalyst surface reconfiguration is vital for revealing the catalytic reaction mechanism under real reation conditions.In this paper,taking the widely used Cu-based catalysts as an example,the surface reconstruction of Cu-based catalysts and related reaction mechanism were systematically studied from four aspects:Cu surface,Cu alloy surface,Cu-metal oxide surface and support induced Cu surface.The surface reconstruction of Cu catalyst occurs in the presence of water vapor.The reconstructed structure is growing along the surface in a bilayer minimum unit structure.The bilayer minimum unit structure is formed by the Cu with adsorbed OH species being pulled up by the OH species to form a new Cu layer,while the Cu with adsorbed O species has not migrate.During CO oxidation reaction,the Cu surface was reconstructed by the synergistic effect of CO and O₂.The strong interaction between CO and Cu increases the crystal lattice of Cu surface,which facilitates the adsorption and dissociation of O₂.The interaction between the dissociated O₂ and Cu makes the Cu surface gradually transform from a crystalline phase to an amorphous phase.Finally,the dissociated O and the adsorbed CO generate CO₂ product and CO₂ rapidly desorb from the catalyst surface.The reaction mechanism was different from the general Mars-van-Krevelen mechanism.Doping Au into Cu system can control the structure and properties of the Cu surface.In the presence of CO and H₂O,the surface reconstruction of Cu Au alloy occurs,resulting in promoting the catalytic activity by the synergistic effect of Cu and Au.Changes in the composition of surface Cu Au can tune the adsorption of CO and H₂O on Cu or Au sites.The surface of Cu Au catalyst was reconstructed to form a periodic structure containing Au components every 4 columns during the reaction conditions.The presence of Au facilitates the dehydrogenation of the*COOH intermediate to form H₂O,but adsorption O species on catalyst surface will inhibit water gas shift reaction.The interaction of Cu with main group metal oxides（In,Sn and Bi oxides）can cause electron reconstruction on the catalyst surface.Cu transfers electrons to the main group metal oxide,and the p orbital energy of main group metal in the reconstructed main group metal oxide has a significant effect on the adsorption of key intermediates in reducing CO₂ to HCOOH.Cu not only actived the active component to adsorb the reaction intermediates,but also played a catalytic synergistic role by tuning the electronic structure of main group metal oxides,indicing in enhancing the reaction activity of CO₂ to HCOOH.ΔG_rdsHCOOH orΔG_rdsHCOOH-ΔG_rdsHER can be considered as the reaction descriptor due to the obvious negative correlation with the experimental catalytic activity.The two-dimensional transition metal carbide or nitride as catalyst support can induce the change the electronic structure for Cu surface.The number of electron obtained by Cu from the support will affect the reaction barrier of rate-controlling step,indicating in tuning the activity of CO₂ reduction reaction.When the transition metals of support are in the same subgroup（IV or VI subgroup）,with the increase of the period of the transition metal,the number of electrons transferred from the support to Cu component increases,thereby inhibiting the reaction of rate-controlling step（*CO desorption）and enhancing the catalytic activity.