Study on in-situ lmmobilization of Size-Controlled Nanoparticles onto Solid Supports

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In this study, we have studied a novel method for immobilization of nanoparticles synthesized in water-in-oil microemulsion onto solid supports. The support were prepared from metal alkoxide in microemulsion, and simultaneously the nanoparticles were in-situ immobilized on the support.First, Rh particle size of Rh/SiO_2 could be controlled in the range between 1.8 and 9.0 nm by changing the types of surfactant and organic solvent used in our method.Next, it was found that some of the Rh particles were partly or wholely embedded in silica supports and that the Rh particle surface were not used in catalytic reaction. Then, we investigated the dependence of the ratio of exposed metal surface to total metal surface (=R ratio) upon several conditions for nanoparticle immobilization. As a result, the R ratio of Rh particles could be increased to be about 80% by shortening the hydrolysis time of alkoxide and decreasing a water content at the hydrolysis. The R ratio of Pd particles in Pd/ZrO_2 also could be increased by a similar manner. Furthermore, in order to increase the R ratio, it was prefarable to immobilize metal complex nanoparticles rather than metal nanoparticles.The metal catalyst immobilized on supports by our method exhibited much higher activity than conventional impregnation catalysts in the hydrogenation of carbon monoxide. In addition, the effect of the R ratio on the reaction rate per an active site were elucidated using the catalysts prepared by our method.