Effect of Acidity and Structures of Supported Tungstophosphoric Acid on its Catalytic Activity and Selectivity in Liquid Phase Synthesis of Ethylbenzene

摘要

As the most important alkylbenzene, ethylbenzene is predominantly synthesized by using acidic zeolite catalysts nowadays. For their environmental benignity and non-corrosive nature, solid heteropoly acids have been used in a variety of catalytic reactions in recent years. Of all the heteropoly acids, 12-tungstophosphoric acid (PW) that has the Keggin structure has the strongest acidity and the highest thermal stability, its acidity is much stronger than that of most inorganic liquid strong acids and acidic zeolites. It has been reported that PW is much more active and selective than zeolite catalysts in alkylation of benzene with 1-dodecene. In alkylation of benzene with ethylene, supported silicotungstic acid has been used as catalyst in liquid phase condition, silica-supported tungstophosphoric acid has only been used under gas phase conditions. In mis paper, we report for the first time of silica-supported PW (SPW) in the liquid phase alkylation of benzene with ethylene and transalkylation of benzene with diethylbenzene. A number of SPW have been prepared by incipient impreghatibn Of mesoporous silica gel pretreated with nitric acid with aqueous solutions of PW. The structures of SPW have been characterized by nitrogen adsorption, Fourier transform infrared spectra (FT-IR), X ray diffraction (XRD), and the acidity characterized by pyridine adsorption FT-IR, programmed temperature desorption of NH_3 (NPD), and Hamett indicators. The catalytic activity and selectivity of SPW in alkylation and transalkylation have been discussed with their acidity and structures.