Highly Dispersed and Active Iron Oxide Nanoparticles in SBA-15 with Different Pore Sizes for the Synthesis of Diphenylmethane

Highly ordered mesoporous SBA-15 catalysts with different pore diameters decorated with various amounts of highly dispersed iron oxide nanoparticles were prepared by using a simple wet-impregnation technique. The structural order of the samples before and after the encapsulation of iron oxide nanoparticles were analysed by X-ray diffraction (XRD), BET nitrogen adsorption, high resolution scanning electron microscopy (HRSEM) and high resolution transmission electron microscope (HRTEM) whereas the nature and coordination of the iron oxide nanoparticles were obtained by ultraviolet-visible diffused reflection spectroscopy (UV-Vis DRS). Characterization results revealed that the iron oxide functionalized samples possess a well-ordered structure and excellent textural properties and the nanoparticles are highly dispersed inside the mesochannels of the SBA-15 supports. The size of the nanoparticles inside the mesochannels was also controlled by tuning the pore diameter of the supports whereas the amount of the nanoparticles was tuned by adjusting the amount of iron source in the synthesis mixture. Finally, these catalysts were tested for Friedel-Crafts benzylation of benzene and other aromatics with benzyl chloride (BC) as alkylating agent under liquid phase condition. All the samples exhibited excellent catalytic performance with a clean BC conversion and the selectivity to diphenylmethane (DPM). The influence of various reaction parameters such as substrate mole ratio, reaction time, reaction temperature and electron donating substituent moieties on the catalytic performance of iron oxide nanoparticles functionalized SBA-15 samples was also investigated. The catalysts showed 100% conversion of BC even at the reaction temperature as low as 50 °C which confirms a higher activity of these catalysts than that of other metal substituted mesoporous catalysts for the benzylation of benzene.