Effect of acidity and structures of supported tungstophosphoric acid on its catalytic activity and selectivity in liquid phase synthesis of ethylbenzene

Silica-supported tungstophosphoric acid (SPW) with Keggin structure in liquid phase alkylation of benzene with ethylene and transalkylation of benzene with diethylbenzene was studied. The structures of SPW were characterized by nitrogen adsorption, FT-IR, and XRD; and the acidic properties characterized by pyridine adsorption FT-IR, NH3-TPD, and Hamett indicators. Tungstophosphoric acid (PW) maintains its Keggin structure in SPW. PW is finely dispersed on the support as the loading less than 30 wt.%. SPW has both Bronsted (B) and Lewis (L) acid sites with B acid sites predominantly. The L acid sites are derived from the chemical interaction between the protons of PW and the hydroxyl groups of silica. The amount and acid strength of surface acid sites of SPW increase as the loading increased. Liquid phase alkylation indicated that catalytic activity of SPW is associated with amount and strength of surface acid sites and dispersivity of PW. Highly dispersed PW is much more effective than bulky solid ones. Liquid phase transalkylation showed that catalytic activity of SPW is determined by amount and strength of surface acid sites. SPW with large amount and strong acid strength of surface acid sites as well as relatively large specific surface areas has high activity in both alkylation and transalkylation. SPW is very active and selective in both alkylation and transalkylation. (C) 2004 Elsevier B.V. All rights reserved.