Fe2O3/TUD-1: an efficient catalysts for Friedel–Crafts alkylation of aromatics

Abstract

Three-dimensional mesoporous (Fe-TUD-1) catalysts with different Si/Fe ratios (100, 50, 20 and 10) are prepared using triethanolamine as template. Physicochemical and textural measurements by XRD, elemental analysis, N2 adsorption, UV–Vis spectroscopy and HR-TEM imaging indicate the formation of pure solid mesoporous materials and the presence of Fe2O3 nanoparticles in the prepared Fe-TUD-1 samples. The catalytic performance of Fe-TUD-1 catalysts is tested in Friedel–Crafts alkylations of single-ring aromatic compounds [e.g. toluene (T), ethyl benzene (EB) and cumene (C)] by benzyl alcohol (BnOH). Dispersion of Fe(III) in the mesoporous matrix of TUD-1 enhanced the catalytic activity of Fe-TUD-1 in the alkylation of aromatic compounds compared to pure Fe2O3 and TUD-1 catalysts. The catalytic activity further increases by the decreasing of Si/Fe ratio. Sample loaded with Si/Fe ratio = 10 (Fe-10) showed almost complete conversion of BnOH in a relatively very short reaction time (<30 min) with 95 % selectivity. The catalytic performance of Fe-TUD-1 was superior to other metal-containing TUD-1 (e.g. Ga, Sn, and Ti) catalysts, or other Fe-containing catalysts (e.g. Fe-MCM-41, ZSM-5 and Fe-HMS). Alkylation of C is the fastest among the three aromatic substrates investigated (at temperatures very close to their boiling points) due to the largest inductive effect by the isopropyl group compared to the methyl group of T and the ethyl group in EB. Dibenzyl ether is formed as a byproduct only in the early times of the reaction and proved to act as alkylating agent after being hydrolyzed backwards to reform BnOH. Leaching experiments show the Fe-TUD-1 materials are very stable and can be reused as alkylation catalyst.