Density Functional Theory Study On Water-Gas Shift Reaction By Rh-EDTA And Rh-Mo₆S₈、Cu Metal Doped Clusters

The water gas shift reaction（Water-Gas Shift Reaction）industrial application has 90 years of history,has been widely used in coal,petroleum and natural gas as raw material of hydrogen production industry and synthetic ammonia industry.In the syngas alcohol,hydrocarbon catalytic process,the low temperature water gas shift reaction is usually used in the methanol reforming hydrogen reaction of CO removal.In recent years,transition metal doped clusters have been the hot topics in the study of low temperature water gas conversion reaction catalyst.Therefore,this paper mainly studies the activity of various doping clusters catalyzing water gas reaction,and provides theoretical guidance for the development of water gas shift reaction catalysts.The main contents as follows:1.We have systematically studied the WGS reaction on various nanosized Cu₁₂TM of Co,Ni,Cu（from the 3d row）,Rh,Pd,Ag（from the 4d row）,Ir,Pt,Au（from the 5d row）on the basis of density functional theory（DFT）calculations.The reaction proposed by Langmuir-Hinshelwood（LH）has been followed,which corresponds to CO^*+OH^*→COOH^*→CO₂+H^*.The comparison of the Gibbs free energy profiles of carboxyl mechanism on different Cu₁₂TM systems concludes that WGS reaction is determined by the steps of H₂ forming and OH^*reacting with CO^*to form COOH^*.Activation barriers（E_a）and reaction energies（ΔH）on a series of Cu₁₂TM show good BEP relationship.What’s more,the energy barrier of rate-determining step of Cu₁₂Au is the smallest.TOF,with the aid of An Energetic Span Model（ESM）,is used to estimate the efficiency of the different Cu₁₂TM clusters.The results show that the values of TOFs in doping Cu₁₂Rh,Cu₁₂Ir and Cu₁₂Pt are smaller than that in pure Cu.Moreover,the values of TOFs in doping Cu₁₂Co,Cu₁₂Ni,Cu₁₂Pd,Cu₁₂Ag,and Cu₁₂Au are higher than that in Cu₁₃.The higher value of TOF,the more favorable catalysts they are.The result shows that Cu₁₂Au is the most efficient in this reaction.Finally,d-band center is used to explain the binding energy of CO and H₂O.It shows that there is a good liner relationship between d-band center and binding energy of CO.2.We systematically investigate the mechanisms of WGSR on [Rh（EDTA）CO]-complex on the basis of density functional theory（DFT）calculations.Two different reaction pathways have been considered:one is the synthesis of HCOOH,and the other is the direct formation of H₂ from H₂O and CO.The former offers new insights into the fundamental direct mechanism for WGSR.In this study,we combine with the energetic span model（ESM）to study the catalytic activity of different active sites（O_a,O_b,O_c,O_d,O_e,O_f,O_g,）and two different reaction pathways.Our calculation results indicate that the formation of HCOOH mechanism is the energetically favorable pathway for the water gas shift reaction on[Rh（EDTA）CO]^-catalyst.Moreover,the O_c site acts as the most active site for the formation of HCOOH due to the highest value of TOF.NPA charges are calculated to shed further light on the properties of Rh.Among with the reaction,the charge of Rh atom varies from 0.452 to0.522e,which shows that the Rh atom lose the electron most to C atom of hydroxyl bond and O atom.In addition,charge of the O-H bond of HEDTA is from-0.121 to-0.339e,which reduces the O-H bond by Rh atom.Combining with the above discussion,we find that the Rh atom is very lively in the reaction.Our work will be useful for developing the WGSR mechanism and designing better catalysts for WGSR.3.The reverse water gas shift（RWGS）reaction catalyzed by Rh-Mo₆S₈ cluster is investigated using density functional theory calculations.Copper-based catalysts are generally considered to be the preferred choice for catalyzing the RWGS.However,with the continuous maturity of various technologies,industrial demand is also increasing.Copper as the catalyst for this reaction,can not meet the conditions of its high temperature,because the copper-based catalyst at high temperatures easily decomposed.Well,we should look for a more suitable catalyst.Through a large number of literature collection,we found that Mo₆S₈cluster structure is stable at high temperature and high selectivity.The reaction is explored along four possible mechanisms:one is the redox mechanism,another is the carboxyl mechanism,the third refers to the formic acid directly decomposing to CO,and the fourth involves the formation of CHO intermediate.Thermodynamic and kinetic data are calculated to consider the catalysis cycle efficiency.Here,we perform the energetic span model（ESM）to investigate the kinetic behavior of the four catalytic cycles.Interestingly,it is shown that the directly decomposition of formic acid is the most suitable pathway for RWGS with highest TOF value and lowest rate-determining energy barrier.We hope that our work will be beneficial to the development of RWGS.