tert-Butylation of Toluene Catalyzed by Phosphotungstic Acid Supported on HBEA Zeolite

The performance of the catalysts prepared by impregnation of phosphotungstic acid (HPW) in HBEA zeolite with different HPW load (HPW(x)/HBEA) was evaluated in alkylation of toluene with tert-butanol with formation of 4-tert-butyltoluene (4-TBT). The obtained results showed that the HPW was highly dispersed on the HBEA support. The specific surface area of HPW(x)/HBEA zeolites decreased along with a decrease in pore volume. The BrOnsted acidity of HPW(x)/HBEA showed a significant increase initially, reaching a maximum at x = 30% and then decreased with further increasing x. The BrOnsted acidity of HPW(30%)/HBEA was 143.0 mol/g, which is an increase of 69.8% when compared with that found for HBEA (84.2 mol/g). The HPW(x)/HBEA zeolite with HPW loading of 30% exhibits the best catalytic activity at 180 degrees C after 4 h. Toluene conversion over HPW(30%)/HBEA reached 73.1% with para-selectivity of 80.9%, which much higher than those found for HBEA (activity of 54.0% with para-selectivity of 69.5%). The improved toluene conversion over HPW(x)/HBEA can be attributed to their higher BrOnsted acidity after loading HPW, while the improved selectivity can be attributed to the narrowed pores of HPW(x)/HBEA catalysts.