Alkylation of toluene with tert-butyl alcohol over HPW-modified Hβ zeolite

An H beta-supported heteropoly acid (H3PW12O40 (HPW)/H beta) catalyst was successfully prepared by wetness impregnation, and investigated in the alkylation of toluene with tert-butyl alcohol for the synthesis of 4-tert-butyltoluene (PTBT). X-ray diffraction, scanning electron microscopy, transmission electron microscopy, fourier-transform infrared spectroscopy, inductively coupled plasma-optical emission spectrometry, the brunauer emmett teller (BET) method, temperature-programmed NH3 desorption, and pyridine adsorption infrared spectroscopy were used to characterize the catalyst. The results showed that loading HPW on H beta effectively increased the B acidity and decreased the pore size of H beta. The B acidity of HPW/H beta was 142.97 mu mol/g, which is 69.74% higher than that of H beta (84.23 mu mol/g). The catalytic activity of the HPW/H beta catalyst was much better than that of the parent HP zeolite because of its high B acidity. The toluene conversion over HPW/H beta reached 73.1%, which is much higher than that achieved with H beta (54.0%). When HPW was loaded on H beta, the BET surface area of H beta decreased from 492.5 to 379.6 m(2)/g, accompanied by a significant decrease in the pore size from 3.90 to 3.17 nm. Shape selectivity can therefore play an important role and increase the product selectivity of the HPW/H beta catalyst compared with that of the parent H beta. PTBT (kinetic diameter 0.58 nm) can easily diffuse through the narrowed pores of HPW/H beta, but 3-tert-butyltoluene (kinetic diameter 0.65 nm) diffusion is restricted because of steric hindrance in these narrow pores. This results in high PTBT selectivity over HPW/H beta (around 81%). The HPW/H beta catalyst gave a stable catalytic performance in reusability tests. (C) 2016, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.