Synthesis of ordered mesoporous silica/ceria–silica composites and their high catalytic performance for solvent-free oxidation of benzyl alcohol at room temperature†
Highly ordered mesoporous Ce-incorporated MCM-41 and MCM-48 silica materials with Ce/Si ratio = 0.1–0.3 have been prepared in a surfactant-assisted hydrothermal method using hexadecyltrimethylammonium bromide (CTAB) as a structure-directing agent (SDA), cerium nitrate hexahydrate and tetraethyl orthosilicate (TEOS) as inorganic co-precursors under basic conditions. Thermal treatment at 823 K has allowed the removal of the organic template, resulting in the formation of long-range ordered 2D hexagonal (p6mm) MCM-41 and cubic (Ia3d) MCM-48, respectively, with ceria-rich particles. Highly ordered mesostructures for Ce-MCM-41 and Ce-MCM-48 materials were characterized with small angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (XRD), nitrogen adsorption–desorption isotherms, UV-visible diffuse reflectance spectroscopy (UV-DRS), transmission electron microscopy (TEM). The elemental compositions were analyzed using elemental mapping from EDS, inductively coupled plasma atomic emission spectra (ICP-AES), X-ray photoelectron spectroscopy (XPS), and solid-state magic angle spinning (MAS) NMR. These high cerium containing mesoporous ceria–silica materials of ∼30 wt% showed an impressive performance in solvent-free highly selective liquid phase oxidation of benzyl alcohol to benzaldehyde at room temperature. This controlled oxidation of primary alcohol to aldehyde over highly stable, completely heterogeneous, non-air sensitive, and reusable Ce-incorporated silica composite can be an excellent gateway for industrial fine chemical synthesis.