Preparation, Characterization And Catalytic Performance Of Silica-Supported Heteropolyacid Catalyst

In this work, heteropolyacid catalysts supported on silica was prepared and characterized, and their performance for catalyzing esterification of 2-butene with acetic acid was evaluated. The silica-supported heteropolyacid and cesium salts of 12-phosphotungstic acid catalysts were prepared by one-step and two-step impregnation methods, respectively. The catalyst skeleton structure, dispersion of active ingredients, specific surface area and pore structure, and acidity and thermal stability of catalysts were characterized by IR, XRD, BET, NH3-TPD, and TG-DTA methods. The esterification reaction of 2-butene and acetic acid was chosen as a model reaction to evaluate catalytic activity and to optimize catalyst preparation parameters. And inactivation of catalysts was also studied.The reaction parameters of direct esterification of 2-butene and acetic acid catalyzed by 12-phosphotungstic acid supported on silica catalyst prepared by impregnation method were optimized. The optimized preparation parameters for supported phosphotungstic acid catalyst were determined by investigation of the esterification reaction of 2-butene and acetic acid. The most favorable esterification reaction parameters determined according to experimental results were reaction temperature of 110℃, alkene/acid ratio of 2, water dosage of 2% and reaction time of 9h, respectively. The most favorable parameters for catalyst preparation were phosphotungstic acid load of 30%, calcination temperature of 250℃,catalyst dosage of 3%, respectively. Under these optimized conditions, the conversion of acetic acid and selectivity of sec-butyl acetate were 35.8% and 93.5%, respectively.The silica-supported cesium salts of 12 - phosphotungstic acid catalyst supported on silica was prepared by two-step impregnation method and characterized by IR, XRD, and TG-DTA. The activity of the catalyst was evaluated by investigation the reaction of 2-butene and acetic acid. Results indicated that the most favorable parameters for preparation of Cs1.7H1.3PW12O40/SiO2 catalyst were load of 30%, calcination temperature of 350℃, and catalyst dosage of 5%, respectively. Under these optimized conditions, the conversion of acetic acid and selectivity of sec-butyl acetate were 42.2% and 91.7%, respectively. The catalytic performance of supported cesium salts of 12 - tungstophoric acid catalyst was briefly superior to supported phosphotungstic acid catalyst.The reason for catalyst inactivation in cycling use was investigated by electric conductivity method together with IR and BET characterization. The silica-supported phosphotungstic catalyst was inactivated after reuse of 3 times, which was mainly caused by dissolve of active ingredients. And silica-supported cesium salts of 12 - phosphotungstic acid catalyst was inactivated after reuse of 5 times, which was mainly caused by the polymers of 2-butene.