Spherical V-MCM-48: the synthesis, characterization and catalytic performance in styrene oxidation

A series of spherical, vanadium-containing, mesoporous V-MCM-48 catalysts with different V/Si atomic ratios were synthesized by a direct hydrothermal method. The structure and morphology of the samples and the states of vanadium in the materials were systematically characterized by XRD, N-2 physisorption, FE-SEM, HRTEM, ICP, UV-vis, V-51 MAS-NMR, ESR and XPS. The possible formation mechanism of spherical V-MCM-48 was proposed based on the Stober process. Simultaneously, the catalytic activities of the samples were evaluated in the oxidation of styrene to benzaldehyde using H2O2 as oxidant. The results show that the V-MCM-48 samples have regular spherical morphology, homogeneous dispersion and highly ordered cubic mesostructure. Characterization results about the coordination states of vanadium species demonstrated that most of vanadium existed as tetracoordinated V4+ species in a silicate framework and a small amount of vanadium as isolated V5+ species on the surface. The prepared spherical V-MCM-48 exhibits much higher catalytic activity in the catalytic conversion of styrene to benzaldehyde. Spherical morphology contributes significantly to the improved catalytic performance of materials. V5+ species on the surface and/or produced from the oxidation of some V4+ in the framework act as active sites. Furthermore, the reaction parameters such as vanadium content in V-MCM-48, molar ratio of H2O2/styrene, temperature, time and solvents were optimized.