Zr(SO_4)_2·4H_2O/SBA-15固体酸催化剂的制备及其催化性能

Preparation and Catalytic Performance of Zr(SO_4)_2·4H_2O/SBA-15 Solid Acid Catalysts

以介孔分子筛SBA-15为载体,采用浸渍法制备了系列四水硫酸锆(ZS)负载型催化剂ZS/SBA-15,用FT-IR、EDS、XRD、N2吸附-脱附、Hammett指示剂等对催化剂的组成、结构和酸强度进行了表征。结果表明,硫酸锆负载后,催化剂仍基本保持六方有序的孔阵列和尺寸不变的介孔孔道;在负载量<40%时,硫酸锆均能在载体上高度分散。该系列催化剂具有中等强度的酸中心,对乙二醇单乙醚与乙酸、正丁醇与柠檬酸的酯化反应有很高的催化活性,且对目标酯产物的选择性为100%。在最佳的负载量和反应条件下,乙二醇单乙醚和柠檬酸的转化率约高达98%,催化剂重复使用多次仍可保持相当的活性。

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.