Preparation of nanosized metal (oxides) by gas phase hydrolysis using mesoporous materials as nanoreactors

Abstract

Immobilized nanosized metal (oxides) on carbonaceous carriers were prepared by hydrolysis under mild conditions by using the carrier pores as a kind of nanoreactor. Metal alkoxide vapor was adsorbed on the carrier and then formed the product upon exposure to water vapor. With this facile method, Titania, Vanadia, Rhodium (oxide), and Platinum (oxide) nanostructures were prepared at high yields, high loadings, and good dispersion in the carrier material. High number concentrations of spheroidal nanoparticles of uniform size (diameter ca. 5 nm) were obtained from less reactive precursors, whereas with highly reactive precursors, such nanoparticles occurred only after subsequent calcination. Nanoparticles appeared to be the thermodynamically stable form of the metal (oxide) produced in the pores. Highly reactive precursors formed metastable seeds, which nucleated and restructured into nanoparticles upon subsequent exposure to heat. The presented method allows for preparation of metal (oxide) nanostructures and effective control of their size and shape.