Abstract:

A series of mesoporous silica SBA-15-supported zirconium sulfate(ZS) catalysts, ZS/SBA-15, were prepared by impregnating hexagonal SBA-15 with an aqueous solution of ZS. The incorporation of ZS in the catalysts was confirmed by infrared spectroscopy(FT-IR) and X-ray energy dispersive spectrometry(EDS). X-ray diffraction(XRD) showed that ZS could be well dispersed on the support until the loading was higher than 40%. N₂ adsorptiondesorption and smallangle XRD were used to characterize the mesostructure of the samples. It was found that the hexagonal order and regular mesopores with unchanged pore size of SBA-15 were mostly retained after ZS incorporation; however, the intensities of XRD peaks of SBA-15 declined, and the surface area and pore volume decreased as the ZS loading increased, suggesting the partial loss of ordered mesostructure due to the impregnation of acidic ZS solution. Acid strength of the catalyst was measured via Hammett indicators. Excellent catalytic performances of these catalysts were observed in the esterifications of acetic acid with 2-ehoxyethanol and citric acid with n-butanol, respectively. The selectivities to desired esters were 100%, and the conversions of both 2-ehoxyethanol and citric acid were as high as 98% under optimal loading level and reaction conditions. The dosages of catalyst, molar ratio of alcohol to acid in reaction mixture and catalyst recycle were also investigated. The activities were decreased slightly during each recycle owing to the solubilization and loss of ZS in water, but could be mostly retained after recycle for several run times.

Key words: zirconium sulfate, SBA-15, catalyst, esterification