Preparation of Metal Oxide-Doped Solid Superacid Catalyst and its Catalytic Performance

A type of SO/sub 4/sup 2/-/ZrO/sub 2/ solid superacid catalyst, doped with aluminum nitrate and ammonium tungstate, was prepared. The flow indictor steam method was performed for acidity measurement of the catalysts, and several characterization techniques, such as XRD, FT-IR, BET, and TGA-DSC, were used for studying the catalytic mechanism. The esterification yield of the modified catalyst was up to 98.9 % for synthesis of n-butyl acetate. The influences of the aging temperature, Al/sub 2/O/sub 3/ZrO/sub 2/ ratio, WO/sub 3//ZrO/sub 2/ ratio, impregnation concentration, and calcination temperature were studied to determine the optimal preparation conditions. The characterization results indicat that, the lower aging temperature was the most important for forming crystal centers on catalyst surface, and getting smaller regular crystal particles; therefore, the bigger specific surface can be available. Suitable calcination temperature can improve the conversion of crystal types, which include tetragonal phase and monoclinic phase. It shows a strong orientation action for formation of useful crystal type by adding W, which also delay the crystallization of ZrO/sub 2/, stable tetragonal phase, and depress the loss of SO42–. It is beneficial to increase the Lewis acid sites on catalyst surface by adding Al/sub 2/O/sub 3/, and the catalytic activity can be improved strongly. The stability of the modified SWZA catalyst is better than that of traditional SO/sub 4/sup 2/-/ZrO/sub 2/ solid superacid catalyst. (author)