DFT Calculation Study On B-doped Cu Surface Catalyzed Water-gas Shift Reaction

In recent years,the energy crisis and environmental problems are becoming more and more serious.With the increasing consumption of fossil fuels,many valuable resources are facing the crisis of depletion.As a new type of secondary energy in the 21 st century,hydrogen energy has attracted wide attention.Water-gas shift reaction is one of the effective means to produce hydrogen energy,which is widely used in catalyst preparation and various industrial processes,among which Cu-based catalysts are widely used in low-temperature water-gas shift reaction.However,the activity in the actual catalytic reaction is too low due to the weak binding ability of pure Cu catalyst to reforming gas.In order to find and design a high activity and high stability catalyst for lowtemperature water-gas shift reaction,a lot of researches have been carried out.In this paper,the structure of pure Cu catalyst was modified by doping B atom on the surface,and the catalytic activity of Cu-based catalyst for water-gas shift reaction was improved.A series of calculations have been carried out on pure Cu surface and B-doped Cu surface by density functional theory(DFT)and first principle.Through the comparison of the activation energy barriers of the rate-limiting steps of the water-gas shift reaction,the main group atom B with the optimal catalytic potential was selected.In addition,it is found that there is a linear relationship between the physical and chemical properties of the main group atoms(Be,B,C),such as electronegativity,atomic radius,specific heat capacity and activation energy barrier of the rate-limiting step.The adsorption behaviors of all reaction intermediates on pure Cu surface and B-doped Cu surface are described.It is found that B atom doping greatly improves the adsorption capacity of all reaction intermediates and all carbon-containing species tend to be adsorbed in the B region.Then,the electronic structures of pure Cu and B-doped Cu surfaces were analyzed in detail.The results show that there are two kinds of heterogeneous Cu atoms with different electronic structures on the surface of B-doped Cu catalyst,which is attributed to the strain effect and ligand effect of heterogeneous Cu atoms.Subsequently,the catalytic reaction mechanism of water-gas shift reaction on pure Cu surface and B-doped Cu surface was designed.Among all the catalytic reaction mechanisms(carboxyl mechanism,redox mechanism,formate mechanism),carboxyl mechanism is the two most potential catalytic reaction mechanisms on the surface.Most of all,after selecting the optimal mechanism,the charge changes of B atomson all reaction intermediates in the reaction path were analyzed along the optimal reaction path.The results show that B atom can be used as a charge transfer hub to promote the charge transfer process between surface and adsorbate,and can transition between anionic state and cationic state.In short,all the calculated results show that the B atom doping greatly reduces the activation energy barrier of the rate-limiting step of the water-gas shift reaction in the Cu-based catalyst,thus improving the catalytic performance of the low-temperature water-gas shift reaction.