Facile synthesis of ultrasmall monodisperse “raisin–bun”-type MoO3/SiO2 nanocomposites with enhanced catalytic properties

Abstract

We report the preparation of ultrasmall monodisperse MoO₃/SiO₂ nanocomposites in reverse microemulsions formed by Brij-58/cyclohexane/water. The nanocomposites are of “raisin–bun”-type with 1.0 ± 0.2 nm MoO₃ homogeneously dispersed in 23 ± 2 nm silica spheres. Characterization is carried out based on transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectrometry (EDS), X-ray powder diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), inductively coupled plasma-optical emission spectrometry (ICP-OES), N₂ sorption measurement, and NH₃ temperature-programmed desorption (NH₃-TPD). The as-prepared MoO₃/SiO₂ nanocomposites are microporous and exhibit enhanced catalytic activities for acetalization of benzaldehyde with ethylene glycol and can be repeatedly used 5 times without obvious deactivation. The catalytic performance improvement is attributed to the unique structure and ultrasmall size of the nanocomposites.