固体超强酸催化剂S_2O_8^(2-)/Fe_2O_3-Al_2O_3的制备及其酯化性能

Preparation of S_2O_8^(2-)/Fe_2O_3-Al_2O_3 solid superacid and its behaviors for esterification

以硝酸铁为铁源、硝酸铝为铝源,通过共沉淀法制备固体超强酸催化剂S_2O_8^(2-)/Fe_2O_3-Al_2O_3。通过催化剂样品的FT-IR谱图、不同焙烧温度催化剂样品的XRD谱图、不同陈化温度的N_2吸附-脱附曲线以及催化剂样品的SEM照片,研究了其晶体的形成过程。催化剂样品红外谱图表明,催化剂中的S=O有较强的共价双键特征,诱导催化剂形成超强酸性;在XRD谱图中既无Al_2O_3的晶相峰,也无Fe_2(SO_4)_3晶相峰,说明Al_2O_3与Fe_2O_3在催化剂样品的表面形成了Al_2O_3-Fe_2O_3共价键的复杂结构。采用BET方程和BJH模型计算催化剂样品的比表面积和孔径分布,经冰水陈化的催化剂样品平均孔径为9.1 nm,最可几孔径为7.5 nm,比表面积为78.9 m^2·g^(-1),孔容0.149 cm^3·g^(-1)。研究了催化剂的铁与铝物质的量比、(NH_4)_2S_2O_8浸渍浓度和不同焙烧温度对硬脂酸正丁酯酯化率的影响。在反应温度85℃、催化剂用量0.2 g(为反应物总质量的2%)和回流反应150 min的条件下,酯化率可达84.5%。

S2O8^2-/Fe2O3-A12O3 solid superacid was prepared by the co-precipitation method using iron （ m ） nitrate and aluminum nitrate as the starting material. Crystallization process of S/O8^2-/Fe2O3-Al2O3 was characterized by FT-IR, X-ray diffraction （XRD）, SEM, nitrogen adsorption-desorption isotherms and pore size distribution measurement. The results indicated by FT-IR spectra that S=O bond was a typical covalent double bond, which induced formation of superacid. XRD results showed that there existed no Al2O3 and Fe2 （ SO4 ） 3 phase in the samples, indicating that a complicated Al2O3-Fe2O3 structure of covalent bond formed. Surface area and pore size distribution of the samples aged in ice water were calculated by BET equation and BJH model, with average pore BET surface area of 78.9 m^2·g^-1 and pore volume size of 9.1 nm, most probable pore size of 7.5 nm, of 0. 149 cm^3 · g^-1 Effects of Fe/Al molar ratio, （NH4） 2 S2O8 concentration and calcination temperature on activity of the catalyst for synthesis of butyl stearate were investigated. Esterification rate of up to 84. 5 % was obtained under the condition as follows： reaction temperature 85 ℃, reaction time 150 min, dosage of the catalyst 2% of total mass of the reactants.