Catalysis Of Polyoxometalate-Protected Gold Nanoparticles

In heterogeneous catalysis, metal-oxide supports play important roles in synthesis and stabilization of highly dispersed metal(O) nanoparticles (NPs). The metal-oxide cluster-anions (polyoxometalates, POMs) are molecular forms of early-transition-metal oxides, which can be used to stabilize metal nanoparticles in solution. The colloidal system (POM-AuNPs) can be regarded as a model of transition-metal oxide supported metal nanoparticles. In this thesis, we have synthesized and characterized the POM-protected gold colloids and studied their catalytic activities. We studied the behavior of POM self-assembly on the surface of gold nanoparticles and demonstrated that charge transfer between POM-gold interfaces leads to the improvement of gold catalytic activity by regulating the electronic structure of gold surface.The contents and outlines of this thesis are as follows:In Chapter one, we have presented a brief introduction of POMs, followed by a brief introduction of the methods of synthesis of gold nanoparticles and their applications, then a literature survey about synthesis of POM-stabilized metal(O) nanoparticles and their applications in catalysis.In Chapter two, we synthesized POM-protected gold colloid and studied its electrocatalytic properties. We found that POM-stabilized Au NPs can reversibly assemble on the electrode surface, resulting in current amplification and quasi-reversible cyclic voltammetric behavior at low ionic strength. We demonstrated the electrocatalytic activity of the POM-protected Au NPs by investigating electrocatalytic oxygen reduction.In Chapter three, we studied the catalytic activity of POM-stabilized Au NPs by the aerobic oxidation of CO. Therein, quantitative information concerning the cocatalyst role of the [(α-PW11O39]7- protecting-ligand on the catalytic activities of gold nanoparticles was investigated. We found that POM-monolayer domains dramatically enhance the activity of gold cores in catalyzing the aqueous-phase aerobic oxidation of CO. Data of X-ray photoelectron spectroscopy demonstrate that charge transfer from the POM ligands to the Au core leads to electro-negative nature of Au, which greatly benefits the activation of O2 and overcomes the limiting step in the catalytic CO oxidation.