Synthetic insertion of gold nanoparticles into mesoporous silica

Industrial catalysts often consist of transition metals supported on microporous or mesoporous high surface area oxides and are prepared by techniques such as impregnation and ion adsorption. In standard fabrication processes the metal particle size is not well-controlled. In this paper we report a new synthetic route for the production of catalyst materials with more precise control of the metal particle size. Gold nanoparticles encapsulated in mesoporous silica (MCM-41 and MCM-48) served as a model system, although the techniques described are applicable to a wide variety of metals and oxide supports. The samples were characterized by a combination of low-angle powder X-ray diffraction, transmission electron microscopy, N-2 porosimetry, infrared spectroscopy, and X-ray absorption near-edge spectroscopy. The results show that the MCM-41 and MCM-48 structures retain their long-range order when metal particles are added; in addition, the size of the channels increases monotonically with metal loading. X-ray absorption near-edge spectroscopy in combination with the adsorption of thiols provides conclusive evidence that 2- and 5-nm-diameter Au nanoparticles are incorporated into the pores of the silicates and that they are accessible to reactant molecules.