Theoretical Study On CO Oxidation Mechanism On Metal Single Atom Catalysts Supported On Pt-Based Transition Metal Sulfides

With the development and use of fossil fuels,the shortage of the earth’s resources and the pollution of the environment have been caused.The development and use of pollution-free and sustainable clean energy is imminent.Proton exchange membrane fuel cell is a new type of energy with high energy density and conversion efficiency.As one of the main components of proton exchange membrane fuel cells,platinum-carbon catalysts have problems such as high cost,low catalytic efficiency,and easy carbon monoxide poisoning,which limit their commercial application.Among them,CO poisoning is one of the main reasons for the reduction of catalytic efficiency of platinum-based catalysts.At present,the prevention of CO poisoning is mainly through the catalytic oxidation of CO at low temperature to remove a small amount of CO gas remaining in the fuel.Therefore,the catalytic oxidation of CO has attracted extensive attention of researchers.Among them,noble metal catalysts have excellent performance,but their disadvantages such as high cost and low efficiency make people have to look for new catalysts to replace them.In recent years,single-atom catalysts have been widely used in various fields due to their high activity,high selectivity,good stability,and low cost.In particular,metal single-atom catalysts supported by two-dimensional materials have made a lot of progress in CO oxidation.In this paper,based on the first-principles calculation method of density functional theory,a single layer of platinum-based transition metal sulfide（PtX₂）containing sulfur vacancies was used as the substrate,and single-atom Ptand Zn were used as active centers to study the catalytic oxidation of CO,respectively.By exploring the Ptsingle-atom CO oxidation process supported on platinum-based transition metal sulfides containing sulfur vacancies,and the roles of three catalyst substrates were revealed in the catalytic process.Then the active source of Zn single-atom catalysts was explored.Our study contributes to the design of highly efficient catalysts with CO tolerance,which provide a reference for the design of highly active Zn single-atom catalysts.The main contents and results are as following:1.The CO oxidation process of single-atom Ptcatalyst supported on sulfur-vacancy of PtX₂（Pt/PtX₂:Pt/PtS₂,Pt/PtSe₂,Pt/PtTe₂）was investigated.The results show that Ptcan be well stabilized on the surface of PtX₂with sulfur vacancy,and the single atoms have different adsorption configurations.The interaction between the substrate PtX₂and single-atom Ptis beneficial to improve the adsorption and catalytic activity of the catalyst for small molecules.Since the adsorption strength of CO is stronger than that of O₂,we investigated the CO oxidation process by TER（Trimolecular Eley-Rideal）and LH（Langmuir-Hinshelwood）mechanisms.The results show that the catalytic oxidation of CO is more likely to proceed through the LH mechanism,and the rate-limiting step is the adsorbing of O₂to form an OOCO intermediate.The reaction barriers are 0.84 e V（Pt/PtS₂）,0.61 e V（Pt/PtSe₂）,and 0.41 e V（Pt/PtTe₂）,respectively,and the activity of the catalysts depends on the adsorption strength of O₂molecules on the substrate.2.The CO oxidation process of single-atom Zn catalyst supported on sulfur-vacancy of PtX₂（Zn/PtX₂:Zn/PtS₂,Zn/PtSe₂,Zn/PtTe₂）was investigated.The results show that the adsorption structures of Zn have qiute obvious features at the vacancies of sulfur-vacancy containing PtX₂,which are attributed to the small atomic radius of Zn.Since the peaks of Zn-d states are mainly at low energy levels,Zn has a weak adsorption energy on the substrate.For the adsorption of reactant small molecule,it is mainly through the hybridization of Zn-p states near the Fermi level.The collective effect of geometry and electronic structure promotes the CO oxidation reaction on Zn/PtX₂via the LH mechanism,with the rate-limiting step being the dissociation of the OOCO intermediate and the formation of the second CO₂.The three catalysts have lower reaction energy barriers,which are 0.36 e V（Zn/PtS₂）,0.27 e V（Zn/PtSe₂）,and 0.31 e V（Zn/PtTe₂）,respectively.Therefore,Zn/PtX₂is a better catalys with CO tolerance.