Theoretical Investigation Of Water Gas Shift Reaction Catalyzed By Ru Halogen Carbonyl Complexes And Single Noble Metal Atoms Dopped Metal Oxide Clusters

With the increase of global energy consumption,hydrogen is considered as one of the cleanest energy sources.Water gas shift reaction?WGSR?has exerted a significant part in hydrogen fuel supply systems for PEMFCs and widespread concern in recent years.Therefore,it is of great importance to study WGSR catalysts with low temperature,high activity and high stability.Therefore,in this paper,we mainly studied the catalytic activity of WGSR catalyzed by ruthenium halogen carbonyl complexes and the single noble metal atom-doping various oxide clusters.These results provide theoretical guidance for highly efficient and low-cost WGSR catalyst synthesis in the experiment.The main contents as follows:1.Density functional theory?DFT?is employed to study the water-gas shift reaction?WGSR?in basic solution for[RuCl₃?CO?₃]^-.Four different mechanistic pathways have been considered.The calculations indicate that formic acid mechanism to be competitive.The energetic span model?ESM?proposed by Shaik et al.has been applied to reveal the kinetic behavior of the four catalytic cycles.Consistent with the above result,the formic acid mechanism yields the largest TOF value(1.89×10^-14s^-1),which is higher than the value of TOF(1.74×10^–16s^–1,Ru?CO?₅;1.88×10^–15s^–1,Fe?CO?₅).It turned out that[Ru?CO?₃Cl₃]^–is a promising candidate for an improved WGSR catalyst and a better catalyst for the industrially important reaction.2.The reversed water gas shift reaction?RWGSR?is an important reaction system that can convert excess CO₂ in the air into CO gas that produce liquid fuels and chemicals.Experimentally,Ru₂Cl₄?CO?₆ catalyzes RWGSR with a very high TON value.Theoretically,few mechanism details have been investigated.Both the energy barrier and the ESM model show that the redox pathway is the best catalytic pathway.The metal-metal coordination of the dinuclear catalyst reduces the energy barrier of the WGSR reaction and therefore has a better catalytic performance than the mononuclear.In addition,we changed the bridge Cl ligand of the original catalyst to a CO ligand to study the ligand effects on catalytic activity.The calculation results show that within a certain range,the smaller the distance between M-M,the stronger the adsorption of small molecules,making the RWGSR catalyze the overall thermodynamic favorable.Among bimetallic catalysts studied,both bimetallic catalysts[Ru??-Cl?Cl?CO?₃]₂ and[Ru??-CO?Cl?CO?₃]₂ shows higher activity than[Ru??-Cl??CO?₄]₂ catalyst with[Ru??-CO?Cl?CO?₃]₂ considering as the most efficient catalyst for RWGS reaction.Therefore,the results of this paper provide new ideas for designing better catalysts for RWGSR.3.This paper systematically studied the catalytic properties of WGSR catalyzed by NM-M_xO_y^±?NM=Ru,Rh,Pd,Ag,Os,Ir,Pt,Au;M_xO_y^±=Al₃O₅⁺,Ce₂O₄⁺,V₂O₆⁺,FeO₃^-,Ti₃O₇^-?.The electronic structure analysis shows that the stability of the cluster is due to the strong hybridization between the d orbital of the noble metal atom and the 2p orbital of the ortho oxygen atom.According to the d-band center theory,the d-band position of Rh-M_xO_y^±closer to the Fermi level lead to the stronger chemical adsorption of CO on the Rh atom,that is,the reaction of Rh-M_xO_y^±with CO is easier.We calculated the redox mechanism of Rh-M_xO_y^±catalyzed WGSR and found that noble metal atoms such as Ru,Rh,Os and Ir listed on the left side of group VIII of the periodic table have a better overall catalytic performance for WGSR.In particular,RhAl₃O₅⁺has a lower energy barrier than RhCe₂O₄⁺.Since CeO₂ is the most promising candidate for WGSR,we speculate that Al₃O₅⁺is another potential cluster for WGSR.These results are expected to provide new guidelines for WGSR to design low-cost,high-performance heterogeneous catalysts.