Synthesis, characterization and catalytic activity of indium substituted nanocrystalline Mobil Five (MFI) zeolite

• In situ modification of the MFI zeolite by incorporation of indium.
• The samples were characterized by XRD, FTIR, TGA, UV–vis (DRS), SAA, EDX and SEM.
• The incorporation of indium was confirmed by XRD, FT-IR, UV–vis (DRS), EDX and TGA.
• Hydroxylation of phenol reaction was studied on the synthesized catalysts.

A series of indium doped Mobil Five (MFI) zeolite were synthesized hydrothermally with silicon to aluminium and indium molar ratio of 100 and with aluminium to indium molar ratios of 1:1, 2:1 and 3:1. The MFI zeolite phase was identified by XRD and FT-IR analysis. In XRD analysis the prominent peaks were observed at 2θ values of around 6.5° and 23° with a few additional shoulder peaks in case of all the indium incorporated samples suggesting formation of pure phase of the MFI zeolite. All the samples under the present investigation were found to exhibit high crystallinity (∼92%). The crystallite sizes of the samples were found to vary from about 49 to 55 nm. IR results confirmed the formation of MFI zeolite in all cases showing distinct absorbance bands near 1080, 790, 540, 450 and 990 cm−1. TG analysis of In-MFI zeolites showed mass losses in three different steps which are attributed to the loss due to adsorbed water molecules and the two types TPA+ cations. Further, the UV–vis (DRS) studies reflected the position of the indium metal in the zeolite framework. Surface area analysis of the synthesized samples was carried out to characterize the synthesized samples The analysis showed that the specific surface area ranged from ∼357 to ∼361 m2 g−1 and the pore volume of the synthesized samples ranged from 0.177 to 0.182 cm3 g−1. The scanning electron microscopy studies showed the structure of the samples to be rectangular and twinned rectangular shaped. The EDX analysis was carried out for confirmation of Si, Al and In in zeolite frame work. The catalytic activities of the synthesized samples were investigated with respect to hydroxylation of phenol, in which catechol and hydroquinone were found to be the major products. It is observed that under all reaction conditions catechol selectivity was higher than the hydroquinone selectivity.In-MFI zeolites were successfully synthesized and were used as an effective catalyst for the hydroxylation of phenol to synthesize catechol and hydroquinone as the major product.

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