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

• Published in: Chinese journal of catalysis 2016-12, Vol.37 (12), p.2134-2141
• Main Authors: Wang, Yuanyuan, Song, Hua, Sun, Xinglong
• Format: Article
• Language: English
• Subjects: Alkylation; B acidity; H3PW12O40; Hβ zeolite; tert-Butyl alcohol; Toluene
• ISSN: 1872-2067; 1872-2067
• DOI: 10.1016/S1872-2067(16)62587-1

An Hβ-supported heteropoly acid (H3PW12O40 (HPW)/Hβ) 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 Hβ effectively increased the B acidity and decreased the pore size of Hβ. The B acidity of HPW/Hβ was 142.97 μmol/g, which is 69.74% higher than that of Hβ (84.23 μmol/g). The catalytic activity of the HPW/Hβ catalyst was much better than that of the parent Hβ zeolite because of its high B acidity. The toluene conversion over HPW/Hβ reached 73.1%, which is much higher than that achieved with Hβ (54.0%). When HPW was loaded on Hβ, the BET surface area of Hβ decreased from 492.5 to 379.6 m2/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/Hβ catalyst compared with that of the parent Hβ. PTBT (kinetic diameter 0.58 nm) can easily diffuse through the narrowed pores of HPW/Hβ, 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/Hβ (around 81%). The HPW/Hβ catalyst gave a stable catalytic performance in reusability tests. The improved catalytic activity over HPW/Hβ can be attributed to higher B acidity after HPW loading on Hβ zeolite. The improved para selectivity can be attributed to the narrower pores in HPW/Hβ.