Synthesis of a mononuclear Ti complex: A molecular precursor strategy for control of silica supported single site Ti decorated Au catalysts for cyclooctene epoxidation

摘要

A mononuclear titanium single crystal C36H40O8Si3Ti was synthesized and designed as a molecular precursor to produce silica supported single site Ti decorated Au catalysts of high activity and selectivity. Single site Ti-O species were successfully deposited onto Au nanoparticles supported on SiO2 by simple grafting procedures. X-ray absorption spectroscopy and diffuse reflectance ultraviolet spectroscopies were used to investigate the structures and chemical natures of the titanium species around gold surface. Increasing the introduction of molecular precursor increased the titanium loading which allowed in-dependent control of Ti loading in the catalyst. When Ti loading increased to 3 wt% the gold NPs was still smaller than 2 nm and the method generated Ti-O units was remained highly dispersed around Au NPs. These samples were further tested as catalysts in selective oxidation of cis-cyclooctene in a stream of O-2. They exhibited excellent catalytic activities and selectivities and the turnover frequencies (TOFs) achieved 83 h(-1). Moreover the catalysts can be retrieved by simple filtering from the reaction pot without diminishment of catalytic activity many times. All in all the results confirmed the important role of both the Au and isolated Ti-O species at the perimeter in the reaction and demonstrated that mononuclear Ti complex was facilitated to produce supported epoxidation catalysts as precursors.