DFT Calculation Study Of Carbon Dioxide Conversion Catalyted By Polyoxometalates-based Catalysts

In this paper,the application of Keggin-type polyoxometalates（POMs）supported Single-Atom catalysts and Dual-Atom catalysts in the capture and conversion of CO₂ is investigated by using Density Functional Theory calculations.The relationship between the electronic structure of the Single-Atom catalysts or Dual-Atom catalysts and their catalytic activity is discussed by investigating the mechanism of the reactions.The specific studies are:（1）The reaction process of α-Keggin-type polyoxometalates-supported Single-Atom catalysts promoting the co-conversion of CO₂ with CH₄ to CH₃COOH was investigated using Density Functional Theory calculations.It was shown that single transition metal active centers tend to be anchored in quadruple sites on the surface of polyoxometalates.Among the nine Single-Atom catalysts,Zn/POMs and Ru/POMs are more effective than the other seven Single-Atom catalysts for the activation of CO₂ and CH₄.Zn and Ru follow different reaction mechanisms in catalyzing the activation of CH₄ due to the different electron occupation states of the d orbitals,and Ru/POMs with the d orbitals in the semi-occupied state of the active center have a relatively higher performance in the activation of CH₄.The Ru/POMs with a semi-occupied d-orbital in the active center have a relatively low kinetic energy barrier in the CH₄ activation process.In addition,activation of CO₂ with Al Cl₃ before reacting with the catalyst can significantly reduce the kinetic energy barrier of the reaction.Combining two methods that can reduce the kinetic energy barrier,i.e.,activation of CH₄ with Ru/POMs Single-Atom catalyst and activation of CO₂ with Al Cl₃ followed by reaction with Ru-CH₃ intermediate.The kinetic energy barrier of the whole co-conversion reaction decisive step can be reduced from 30.43Kcal-mol^-1 to 20.88 Kcal-mol^-1.（2）The reaction process of γ-Keggin-type polyoxometalates-supported Dual-Atom catalysts in the electrocatalytic reduction of CO₂ to C₂ products was studied using Density Functional Theory calculations.It is shown that the two transition metal active centers show a high-low configuration when anchored on the polyoxometalates surface due to the steric effects,but this structural difference has little effect on the ability of transition metals to activate CO₂.The Re₂-POMs with the best CO₂ activation effect has C₂ products selectivity.Among the four products catalyzed by Re₂-POMs for the reduction of CO₂ to C₂,the yields of the products ethanol and ethylene glycol were significantly higher than those of ethyl ene and ethane,while the selectivity of ethanol was much higher than that of the ethylene glycol product among the dominant C₂ alcohol products.