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

在本研究中，我们研究了一种将油包水微乳液合成的纳米颗粒固定在固体载体上的新方法。采用微乳液法制备了金属醇盐作为载体，同时将纳米颗粒原位固定在载体上。首先，通过改变表面活性剂和有机溶剂的种类，可以将Rh/SiO_2的粒径控制在1.8 ~ 9.0 nm之间。其次，发现部分Rh颗粒部分或全部嵌入二氧化硅载体中，并且Rh颗粒表面未用于催化反应。然后，我们研究了几种纳米颗粒固定条件下暴露金属表面与总金属表面的比例（=R比）的关系。因此，通过缩短醇盐水解时间和降低水解时的含水量，可将Rh颗粒的R比提高到80%左右。Pd/ZrO_2中Pd粒子的R比也可以通过类似的方法提高。此外，为了提高R比，固定化金属复合纳米颗粒比固定化金属纳米颗粒更可取。在一氧化碳加氢反应中，用该方法固定在载体上的金属催化剂表现出比传统浸渍催化剂更高的活性。此外，还利用该方法制备的催化剂考察了R比对活性位点反应速率的影响。

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.