SiO_2或TiO_2改性S_2O_8~(2-)/ZrO_2固体超强酸的结构及其催化性能

利用共沉淀法合成了S2O82-/ZrO2-SiO2(SZS)和S2O82-/ZrO2-TiO2(SZT)固体超强酸催化剂,通过XRD,FTIR,SEM对催化剂进行了表征;以酯化反应为探针,考察了催化剂的配比、浸渍液(NH4)2S2O8的浓度、浸渍时间及焙烧温度对酯化率的影响,初步探讨了SiO2或TiO2改性对S2O82-/ZrO2固体超强酸的结构和催化活性的影响。实验结果表明,SiO2或TiO2的引入对ZrO2的晶化和催化活性有不同的影响,引入SiO2比引入TiO2更易于覆盖催化剂的酸中心,且引入TiO2的SZT催化剂比引入SiO2的SZS催化剂更容易被S2O82-溶解形成硫酸盐;焙烧温度高于500℃后,固体酸表面的硫物种流失严重,同时由于SZS催化剂形成的晶面,因此SZS催化剂的活性比SZT催化剂下降明显。

Structure and Catalytic Performance of S2O82-/ZrO2 Modified by SiO2 or TiO2

Solid superacids S2O28-/ZrO2-SiO2(SZS) and S2O28-/ZrO2-TiO2(SZT) were prepared by coprecipitation and then impregnation,and characterized by means of XRD,FTIR and SEM.Their catalytic activities in the esterification of stearic acid and butanol to butyl stearate were studied.The effects of n(Zr(NO3)4)∶n(Na2SiO3/C16H36O4Ti),concentration of impregnating solution((NH4)2S2O8),impregnating time and calcining temperature on the catalyst activity were investigated.The results showed that there were the different effects of SiO2and TiO2 modifications on the crystallization and catalytic activity.Covering the acidic sites with SiO2 is easierthan that with TiO2,while SZT catalyst is more liable to being dissolved by S2O28-into sulfates than SZS catalyst.In addition,the sulfocompounds on the solid superacids run off seriously when the calcining temperature is higher than 500 ℃ and the catalytic activity of SZS drops more severely than that of SZT due to the effect of the crystal face.