Theoretical Studies On Structures And Catalytic Properties Of Complexes And Clusters With Group 10-11 Elements

Complexes and clusters with group 10-11 elements have attrated tremendous attentions due to their broad applications in industrial synthesis and catalysis.Gold and palladium systems have extraordinary optical,electronic and catalytic properties and exhibit excellent catalytic performances in various reactions,such as synthesis of H₂O₂,oxidation of CO,methane,and alcohols,water-gas shift,vinyl acetate synthesis and hydrogenation of 1,3 butadiene.However,there is still lack of deep inverstigations on the importance of electronic structures and chemical bondings in the catalytic performances of metal complexes and clusters.The consequence of metal-metal and metal-ligand interactions on the geometry structures and properties is also noteworthy.In the present work,we performed calculations based on density functional theory and ab initio molecular dynamic methods to study the influence of geometry structures,electronic structures and bonding properties on the catalytic performences of metal complexes and clusters with group 10-11 elements.Our work aims at offering insights into the nature of homogeneous and heterogeneous catalytic reactions as well as design of new efficient catalysts.Systemetic investigations of[MX₂]^-?M=Cu,Ag,Au,Rg;X=H,Cl,CN?complexes with group 11 elements show that both electronic structures of the metal and electronegativity of the ligand play vital roles in determining the bonding properties of metal-ligand.It reveals that the covalency of the M-X bond is enhanced by the strong relativistic effects of Au and Rg atoms.As the atomic number of the metal atom increases,spin-orbit splitting becomes larger.Besides,the covalency also increases with decreased electronegativity of the ligand.A series of theoretical studies on the trinuclear clusters[M₃X₃?PPh₃?₃]⁺?M=Ni,Pd,Pt;X=F,Cl,Br,I?with group 10 elements indicate that electrons of the??M₃?orbital are oxidized due to the strong interactions between the trimetallic center and the ligands,with the oxidation state of M₃ equal to+4.Therefore,metallic?-aromaticity is found in this cluster.We have shown that the stability and the catalytic activity of the trinuclear clusters can be tuned by altering the energies and compositions of the metal-metal and metal-ligand chemical bonding orbitals.Relativistic effects are also of great importance in determining the activity of H₂ adsorption.An Ab initio molecular dynamics study of Au₃₂Pd₆ nanoparticles under reaction conditions shows that high temperature,adsorption of hydrogen atoms at the alloy surface and support will result in structural rearrangement,where Pd atoms migrate from core to the surface of the cluster and break the Pd₆@Au₃₂ core-shell structure.Pd atoms at the cluster surface can be stabilized by hydrogen adsorption because of strong interactions between Pd and H atoms.The flattened shape of the cluster is observed with TiO₂ support due to the interactions between the cluster and the support.Compared to stoichiometric surface,the cluster can forms stronger bond at the surface with point defects.The charge transfer between the support and the cluster is in the opposite direction when the support is reduced and oxidized.Under reducing conditions,charge transfers to the cluster and more M-Ti bonds are formed.However,under oxidizing conditions,charge transfers to the surface and more M-O bonds are formed.The stability of single atom alloy Au₃₇Pd₁ is highly dependent on the bond strength of Au-Pd.Both CO and O₂ adsorption prefer the vertex sites at the alloy surface,where the metal-metal bond is weaker than the core and centroid sites.CO adsorption is more favorable compared to O₂.CO oxidation reaction of the cluster is easy to occur,with the highest activation barrier lower than 0.85 eV.