Mesoporous titanosilicate-silica-coated cobalt ferrite core-shell catalysts for the oxidation of styrene

Mesoporous titanium silica-coated cobalt ferrite core-shell structures were synthesized as catalysts for styrene oxidation by hydrothermal and sol-gel methods. The catalysts were characterized by XRD, AA, SEM, TEM, FTIR spectroscopy, N2 physisorption, ICP-OES and XPS. XRD patterns indicated that the magnetic core was composed of cobalt ferrite. SEM and TEM micrographs along with the IR spectra confirmed the presence as desired of a dense SiO2 layer on the core. XPS revealed that the outest layer of the structure was made of a mesoporous Ti-SiO2 layer. The successful incorporation of Ti active oxidation sites (framework Ti, FW Ti) in the mesoporous layer was verified by XPS Ti 2p spectra decomposition. The post-grafting method for the Ti insertion proved to be better than the one-pot to obtain a higher number of active Ti sites on the surface. All the synthesized catalysts were active in styrene oxidation with dilute aqueous H2O2. The highest styrene conversion (37%) was obtained with the catalyst synthesized by post-grafting of Ti on a preformed mesoporous SiO2 layer with a high specific surface area. This catalyst was the one with the highest fraction of surface FW Ti (XPS). The major products of the reaction were benzaldehyde and phenyl acetaldehyde. The catalyst was easily recovered from the reaction medium using an external magnet, and no significant loss of activity was observed after four catalytic cycles.