Cage type mesoporous ferrosilicate catalysts with 3D structure for benzylation of aromatics

The Friedel–Crafts benzylation of benzene and various substituted benzenes employing benzyl chloride as an alkylating agent over a series of three-dimensional cage type mesoporous ferrosilicate (FeKIT-5) catalysts was investigated. These FeKIT-5 materials with different nSi/nFe and ratios were synthesized hydrothermally using polymeric pluronic F127 surfactant in a highly acidic medium and characterized using various physicochemical techniques. The characterization results confirmed that the prepared materials exhibit a well-ordered 3D porous structure with cage type pores and excellent textural characteristics such as high surface areas (935–1130 m2 g−1) and large pore volumes (0.57–0.76 cm3 g−1). The unit cell constant of the samples increased with increasing the iron content of the samples, confirming the incorporation of iron in the silica framework structure of KIT-5. UV–vis results revealed that most of the Fe atoms in FeKIT-5 are in tetrahedral coordination and occupy framework position. It was found that the iron incorporated mesoporous silica materials exhibited a high conversion and selectivity for benzylation under liquid phase condition. The influence of various parameters such as temperature, time on stream, nBenzene/nBC ratio and the nSi/nFe ratio of the catalyst affecting the activity of the catalyst on the benzylation of benzene using benzyl chloride was investigated. The study was also extended to the benzylation of toluene, p-xylene, mesitylene and anisole in order to check the catalytic performance of the catalyst over different electron donating substituents. The reaction kinetics of benzene benzylation over FeKIT-5 catalyst was also investigated. The catalytic activity of FeKIT-5 catalyst was also compared with AlSBA-15, FeHMS and pure mesoporous silica KIT-5. Among the catalysts studied, FeKIT-5(7) showed the highest activity with a complete conversion of benzyl chloride and 100% selectivity to diphenylmethane in 35 min under the optimized reaction condition.

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► Synthesis of iron substituted cage type mesoporous silica FeKIT-5.
► The prepared catalysts exhibit a high surface area and large cage type pore diameter.
► Benzylation of benzene over Fe-KIT-5 with different iron contents.
► The catalyst offered excellent conversion and a high selectivity to diphenylmethane.