Mesoporous gallosilicate with 3D architecture as a robust energy-efficient heterogeneous catalyst for diphenylmethane production

Abstract

Herein, we report the preparation of 3D mesoporous gallosilicate with Ia3d symmetry (GaKIT-6) and different gallium contents using Pluronic P123. The incorporation of gallium into the silica framework of KIT-6 is difficult if the usual synthesis method of KIT-6 is followed, because it requires a large amount of HCl in the synthesis mixture. Therefore, the amount of HCl in the synthesis mixture is reduced to suitably adjust the solution pH so as to incorporate a large amount of gallium into the silica framework of KIT-6. The low-angle powder XRD results confirm that all the samples demonstrate well-ordered and a cubic 3D structure with Ia3d symmetry. However, the wide-angle XRD patterns show no peaks at the higher angle, which confirms the absence of gallium oxide nanoparticles in the nanochannels and the incorporation of gallium atoms into the silica framework. The nitrogen adsorption and electron microscopy studies reveal that the samples demonstrate excellent textural features with well-ordered mesoporous structures having spherical morphology. The analysis of the solid-state 29SiMAS NMR spectra confirms that the gallium atoms are bonded tetragonally with the silica framework of KIT-6. Furthermore, the catalytic performance of the materials has been investigated in the benzylation of benzene, with benzyl chloride as a benzylating agent. The catalytic activity of GaKIT-6 increases with an increase in gallium content in the catalyst. GaKIT-6 with a Si/Ga molar ratio of 7 demonstrates much better catalytic activity than do several reported 1D and 2D heteroatom-incorporated mesoporous materials. In addition, the GaKIT-6 catalyst is found to be highly active even at reaction temperatures as low as 313K, which demonstrates a high benzyl chloride conversion and diphenylmethane selectivity. The catalytic activity of the GaKIT-6 catalyst is retained even after the recyclability test, which confirms that the GaKIT-6 catalyst is highly stable and can be used thrice without affecting its structural order. © 2013 WILEY-VCH Verlag GmbH & Co.