Oxidation Catalysis of Au Nano-Particles Immobilized on Titanium(IV)- and Alkylthiol-Functionalized SBA-15 Type Mesoporous Silicate Supports

Novel Au nano-particle catalysts immobilized on both titanium(IV)- and alkylthiol-functionalized SBA-15 type ordered mesoporous silicate supports were developed. The bi-functionalized SBA-15 type support could be synthesized by a one-pot method. To the synthesized supports, Au was immobilized by the reaction of the alkylthiol groups on the supports with AuCl4-, following reduction with NaBH4. The immobilized amount and the formed structures and the electronic property of the Au species depended on the loading of alkylthiol. The moderate size (2-3 nm) nano particulate Au sites formed on Ti(0.5)-SBA(SH)(0.5) were negatively charged. The aerobic alcohol oxidation activity of the catalysts depended on the loading of alkylthiol and the structure of the Au nano-particles. The non-thiol-functionalized catalyst (Au/Ti(0.5)-SBA(SH)(0)) composed of the large (5-30 nm) and the higher thiol-loaded catalyst (Au/Ti(0.5)-SBA(SH)(8)) composed of the small cationic Au species were almost inactive. The most active catalyst was Au/Ti(0.5)-SBA(SH)(0.5) composed of the electron-rich Au nano-particles formed by the electron donation from the highly dispersed thiol groups. Styrene oxidation activity in the presence of 1-phenylethanol with O-2 depended on the loadings of titanium(IV) on the Au/Ti(x)-SBA(SH)(0.5). The titanium(IV) sites trapped the H2O2 generated through the alcohol oxidation reaction, and also contributed to the alkene oxidation by activating the trapped H2O2.