蒙脱土负载型固体酸催化剂的烷基化性能与结构研究

Structural Characterization and Catalytic Properties of Montmorillonite-Supported ZnCl_2 Solid Acid Catalysts

以酸化后蒙脱土为载体,采用浸渍蒸发法制备了环境友好的蒙脱土负载ZnCl2型固体酸催化剂。研究了蒙脱土酸化处理、ZnCl2负载量及活化温度对催化剂烷基化活性的影响,并初步考察了催化剂的稳定性,比较了几种不同酸催化剂的烷基化活性。利用XRD、BET、TG-DTA、吡啶吸附FTIR对催化剂的结构进行了表征和测定;结果表明,蒙脱土酸化处理后形成的孔道有利于负载ZnCl2, ZnCl2与蒙脱土的羟基之间存在着化学键合,经活化后转化成Zn(OH)Cl。蒙脱土负载ZnCl2后明显地提高蒙脱土表面的总酸量,催化剂活性与其表面总酸量之间有关,催化剂表面L酸与B酸的共存有利于其烷基化活性的提高。实验条件下,蒙脱土负载ZnCl2型催化剂在苯与氯苄的烷基化反应中表现出较高的催化活性,二苯甲烷的收率最高可达83.6%。与其它Lewis酸试剂及酸化蒙脱土相比,蒙脱土负载型催化剂催化活性大有提高。

By using acid-treated montmorillonite as catalyst supporters, environmentally friendly montmorillonite-supported ZnCl2 solid acid catalysts were prepared through impregnation-evaporation method. The effect of different acid-treated conditions, ZnCl2 loading and activated temperature on catalytic alkylation activity of montmorillonite-supported catalysts was examined. The stability of supported reagent catalysts was also investigated, and the comparison of alkylation activity between traditional acids and supported catalysts was conducted. The structure and surface properties of montmorillonite-supported ZnCl2 solid acid catalysts were characterized by the techniques such as XRD, BET, TG-DTA and pyridine adsorbed FT-IR techniques. Results show that the new porous structure of montmorillonite, which is favorable for supporting ZnCl2, can be created by the suitable acid treatment. It has been found that there is a chemical reaction between montmorillonite supporter and ZnCl2. ZnCl2 supported on montmorillonite has connected with the Si-OH group of montmorillonite through chemical bonds, and then converted into a new species Zn(OH)Cl at activated temperature. Montmorillonite supported ZnCl2 reagent has remarkably increased the total acid amounts on the surface of supporter. FI-IR results indicated that the coexistence of Lewis acid and Bronsted acid on the surface of montmorillonite is conducive to the enhancement of catalytic alkylation activity of catalysts. A high conversion of benzyl chloride up to 83.6% over montmorillonite supported ZnCl2 catalyst in the benzylation of benzene with benzyl chloride was obtained under experimental condition. Compared with traditional acids, montmorillonite supported ZnCl2 catalysts show a remarkably high alkylation activity.