Sol-gel法制备SO_4^(2-)/ZrO_2-SiO_2及催化合成对硝基苯甲酸甲酯的研究

Study on SO_4^(2-)/ZrO_2-SiO_2 Prepared by Sol-gel Method and Its Activity on Catalytic Synthesis of Methyl p-Nitrobenzoate

以ZrOCl2·8H2O和正硅酸乙酯(TEOS)为原料,采用溶胶-凝胶法和透析法制备固体超强酸SO42-/ZrO2-SiO2催化剂,考察了制备条件对硅、锆凝胶化时间的影响,并以合成对硝基苯甲酸甲酯为探针反应,研究了催化剂制备条件对催化活性的影响,最后采用Hammett指示剂法、BET法、FT-IR、TEM和XRD分别对催化剂的酸强度、比表面、反应前后骨架结构和形貌变化、晶相进行了表征。结果表明:(1)当水浴温度为80℃,水10mL时,锆凝胶化时间最短;(2)水浴温度为80℃,水8mL,pH=3.0-4.0时硅凝胶化时间最短;(3)当硅、锆原子摩尔比为10:1,H2SO4浸渍液浓度为1.0mol·L-1,焙烧温度550℃时,催化剂的活性最高,酯产率为70%左右;(4)催化剂酸强度Ho<-12.70,反应前后催化剂比表面变化较大且结构形态存在较大差异,催化剂中的SiO2为无定形态,ZrO2为四方晶态。

The preparation conditions of zirconium and silicone gel that for preparing solid superacid SO4^2-/ZrO2-SiO2 catalyst by sol-gel and dialysis method that from ZrOCl2·8H2 O and TEOS were investigated. The effect of preparation conditions on catalytic activity were also studied using the synthesis of methyl p-nitro benzoate as a probe reaction. The characters of catalyst including a-cidity,specific area,structure transformation after reaction,and crystalline phase was tested by Hammett indicator,BET method,FT-IR,TEM and XRD respectively. The results show that the shortest time for preparing zirconium gel were as follows：temperature of water bath was 80℃,water 10mL,and for preparing silicone gel were 70℃,8mL and pH=3. 0-4. 0. Under the conditions that the molar ratio between zirconium and silicon was 10：1,concentration of H2 SO4 solution was 1. 0mol·L^-1 ,calcination temperature was 550℃,the catalyst had high performance. The catalyst was solid superacid as its Ho〈-12. 70 and had suitable specific area. The structure of catalyst often changes greatly after reaction according to FT-IR and TEM. The SiO2 containing in catalyst was amor-phous,and tetragonal for ZrO2.