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.
