Cerium Containing MCM-41-Type Mesoporous Materials and their Acidic and Redox Catalytic Properties

Abstract

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 (∼600 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), N2 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 m2 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.