Theoretical Study On The Structure And Catalytic Properties Of The Noble Metallic Clusters

The CO oxidation over noble metallic nanoparticles is generally described by a bi-molecular reaction mechanism involving the interactions between single CO and O₂ molecule. In this work, we have examined the role of the co-adsorbed CO molecule played in CO oxidation reaction by studying the CO oxidations over two kinds of model noble metal clusters, namely, the icosahedra M₁₃?M = Au, Ag, Cu, Pt, Pd? and hetero-atom doped Au₁₈M?M = Ag, Cu, Pt, Pd? clusters, on basis of density functional theory?DFT? calculations. The results indicate that the co-adsorbed CO molecule at a triangular active site can induce the dissociation of the OCOO* intermediate via a tri-molecular reaction route. The reaction rate analysis using a simplified micro-kinetics model suggests that the tri-molecular reaction routes have higher reaction rate than the conventional bi-molecular route on most hetero-atom doped Au₁₈M clusters. The underlying reason of promoting oxidation effect of co-adsorbed CO molecule is unraveled. It is found that the relatively weaker d-?* back bonding of CO on group ten elements like Au, Ag and Cu may increase its electrophilic activity, which can facilitate the dissociation of nearby OCOO* intermediate. For the CO molecule that is bounded to the Pd and Pt atoms, it can induce the dissociation of OCOO* intermediate either, but shows weaker electrophilic activity. By explicitly considering the elementary reaction steps into a Kinetic Monte Carlo?KMC? simulation, we have shown that the tri-molecular reaction route is an alternative reaction channel of CO oxidation, which is competitive to the conventional bi-molecular route on doped Au₁₈M cluster. These results may provide new insights into fundamental mechanism of CO oxidation over different noble metal nanoparticles as well as their alloy clusters.For the structural transition path prediction of enantiomers of Au₃₈?SH?₂₄, Au₃₆Pt₂?SH?₂₄ and Au₃₆Pd₂?SH?₂₄ ligand- protection cluster, follow the?1?:The reaction is strictly intramolecular, and the addition of thiols does not affect the mechanism.?2?:The activation entropy is very close to zero, which suggests a mechanism that is in accordance with a least-motion principle. We propose that the Au₃ triangular atom of the Au₂₃ gold core can rotate around the main axis of the spindle for small amplitude with low energy rotation, and the associated ligands also rotate with small amplitude, thereby realizing the structural transformation of the leftright handed. By DFT calculations and drawing energy curve, we found that Au₃₈?SH?₂₄, Au₃₆Pt₂?SH?₂₄ and Au₃₆Pd₂?SH?₂₄ antipodal structure transition path required the highest energy barrier were between the 30kcal/mol and 40kcal/mol, which is higher than experimental observation value 28kcal/mol. Therefore, in the next step of the research, we will further optimize the calculation methods and binding kinetics simulation, to determine the applicability of the proposed path, and provide people a theoretical guidance or help for other chiral thiol ligands of gold nano structure transformation and the actual application of protection.