Cerium containing MCM-41-type mesoporous materials and their acidic and redox catalytic properties

The syntheses of cerium containing MCM-41 mesoporous molecular sieves (Ce-MCM-41) were carried out using different hydrothermal methods. However, the Ce-MCM-41 samples were mainly prepared by refluxing the gel mixture at atmospheric pressure under stirring (similar to600 rpm). For comparison, the syntheses were also carried out in autoclave under autogeneous pressure both in static and in stirring conditions. Powder X-ray diffraction (XRD), N-2 adsorption, diffuse reflectance UV-visible (UV-vis) spectroscopy, IR spectroscopy, solid state magic-angle spinning nuclear magnetic resonance spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectrometry (EDX), transmission electron microscopy and thermogravimetric analyses of the samples reveal that well-ordered MCM-41-type mesoporous materials were prepared and Ce is incorporated presumably into the framework position and/or into the walls of silica matrix of MCM-41 structure. The EDX analyses of the samples confirm the presence of Ce in the Ce-MCM-41 samples. Typical XRD patterns of MCM-41-type hexagonal structures and high BET surface areas (983-1414 m(2) g(-1)) with isotherms of type IV of these materials indicate the presence of hexagonal mesopores in the samples. The presence of a strong absorption band centered at ca. 300 nm and the absence of any absorption band at ca. 400 nm in the diffuse reflectance UV-vis spectra indicate the presence of tetra-coordinated cerium in the silica network of Ce-MCM-41 samples. The Ce-MCM-41 samples are active as catalysts for vapor-phase dehydration of cyclohexanol to cyclohexene and hydroxylation of 1-naphthol with aqueous H2O2 and tert-butyl hydroperoxide. :, (C) 2002 Elsevier Science (USA).