The Catalytic Properties Of Copper-zirconium Nanoalloy Clusters By First Principles Calculation

Since the industrial age,the massive combustion of fossil fuels such as coal,oil,and natural gas has caused a sharp increase in the carbon dioxide(CO₂)content in the air and caused the greenhouse effect.The rapid consumption of fossil fuels as a non-renewable resource makes people have to consider looking for a clean and efficient renewable energy source to achieve the sustainable development of human society.Capturing CO₂ as a carbon source and using renewable energy such as solar energy,wind energy,and hydropower as energy to convert CO₂ into valuable chemical products is an important technical approach to realize a low-carbon economy.The transition metal copper(Cu)and its alloy materials have excellent performance as a catalyst in the catalytic reduction of carbon dioxide.The zirconium-doped cooper(Zr-doped Cu)cluster catalyst has been proved to be an ideal catalyst in the catalytic reaction of carbon dioxide hydrogenation to methanol.Although it has been found experimentally that the addition of Zr in the Cu catalyst promotes the synthesis of methanol,the specific reaction mechanism and the influencing factors of the change in catalytic activity are still unclear,especially the lack of systematic theoretical research on the catalyst itself.In this paper,the first principles calculation based on density functional theory(DFT)was used to investigate the effects of Zr atom site,cluster size and cluster composition changes in Zr-doped Cu icosahedral clusters on the catalytic performance of the hydrogenation of carbon dioxide to methanol,providing theoretical guidance for the preparation of high-performance catalysts.The main tasks are as follows:1.The role of Zr atoms in the Zr-doped Cu clusters on improving the catalytic performance of the clusters was studied,and the influence of of Zr atom site changes was preliminarily discussed.The reaction of CO₂ hydrogenation to CHO was studied on pure Cu clusters(Cu₅₅),Cu clusters doped with Zr atom(Cu₅₄Zr),and bulk Cu surfaces doped with Zr atom(Cu(111)/Zr).The results show that the doping of Zr atom in the Cu clusters enhances the adsorption of reactant CO₂ and reduces the activation energy of the dissociation of H₂ to H atoms and the hydrogenation of CO₂ to CHO.Compared with Cu(111)/Zr,the Cu₅₄Zr clusters exhibit stronger adsorption to adsorbates and has a lower activation energies in the reduction of CO₂ to CHO.The study on the doping sites of Zr atoms found that for the reaction of CO₂hydrogenation to CHO,the Zr atoms exhibited higher catalytic activity at the edge site than at the vertex.2.The catalytic performance of the reaction of CO₂ hydrogenation to methanol on different sizes of Zr-doped Cu clusters has been studied.The icosahedral Cu clusters with atom numbers of 13,55 and 147 were constructed.The doping sites of Zr atoms in Cu clusters include vertex('v'),edge('e')and facet('f').The adsorption energy of the adsorbate and the activation energy of the reaction process are calculated.The results show that in the Zr-doped Cu clusters of the same size,the Zr atoms doped at the edge site show the most favorable adsorption of adsorbates and the high catalytic activity for methanol synthesis reaction.The charge analysis shows that when Zr atoms are doped in the edge site,more electron exchange occurs between the catalyst and the adsorbate.When the site of Zr atom is constant,with the increase of the cluster size,the activation energy changes of different reaction steps in the methanol synthesis reaction process are become complicated.In all Zr-doped Cu clusters,hydrogenation of H₃CO to CH₃OH was identified as a rate limiting step,and its activation energy decreased with the increase of cluster size.3.Explore the effect of changes in the composition of the Cu Zr clusters on the reaction of CO₂ hydrogenation to methanol.An icosahedral cluster composed of 55 Cu atoms was selected as the research model,and 1,12,30 and 42 Cu atoms were replaced with Zr atoms,respectively.The adsorption analysis of the reactants showed that when the number of Zr atom increases,the site near Zr atom is still the main choice of the adsorption site for these adsorbates,and moreover the site connected with more Zr atoms is gradually formed and acts as the main adsorption site.The smaller the distance between the adsorbate and the surface of the cluster,the stronger the adsorption.Moreover,the reaction path of CO₂ hydrogenation to methanol with Zr composition varying.When Zr atom number is 1 or 12 in Cu Zr NPs,the reverse water gas shift and CO hydrogenation(RWGS+CO hydro)path is chosen,while it is Formate path when Zr atom number is 30 or 42.In this two path,the step of H₃CO hydrogenation to CH₃OH is confirmed to be rate limit one for these four Cu Zr NPs.And moreover,the corresponding activation energy barrier is found to be smallest in Cu₂₅Zr₃₀ NP.Interestingly,in the whole process of CO₂ conversion to CH₃OH,the activation energy for each step is almost always smaller in Cu₂₅Zr₃₀ NP if compared with other Cu Zr NPs.In addition,the byproduct of CO is well suppressed in this catalyst,and so Cu₂₅Zr₃₀ NPs show their great potential with good catalytic activity and selectivity for CH₃OH synthesis.