具有多级孔结构的丝光沸石的合成与性能研究

以表面活性剂十六烷基三甲基溴化铵(CTAB)作为模板剂, 在不添加晶种和有机共溶剂的情况下采用简单的一步水热合成法制备了含有2~4 nm介孔的多级孔纳米丝光沸石。 通过改变 CTAB引入量可以调节所得多级孔丝光沸石样品的外比表面积以及介孔孔容, 最大外比表面积和介孔孔容可分别达到191 m²/g和0.17 cm³/g。均三甲苯在丝光沸石样品上的吸附行为表明, 微孔丝光沸石仅能吸附少量的吸附质, 而多级孔丝光沸石吸附量较大, 并呈现出IV型等温线的特征, 展示出多级孔丝光沸石中介孔的特征。以均三甲苯与苄基氯的苄基化反应来考察多级孔丝光的催化性能。相比于传统微孔丝光沸石, 苄基化反应在多级孔丝光沸石的转化率提高了近7倍, 反应的表观速率常数提高了近19倍。这是由于多级孔丝光沸石较高的外表面积和介孔孔容可以有效地改善大分子反应物的可接近性和产物的传质速率, 从而提高了大分子催化反应的效率。

Synthesis and Characterization of Hierarchical Mordenite Zeolite

Hierarchical MOR zeolite nanocrystallines with mesoporous architecture composed of 2~4 nm pores were synthesized via a simple hydrothermal route by adding surfactant CTAB as mesoporous template in the absence of organic co-solvent and zeolite seeds, in which the mesoporous volume and external surface area could be adjusted by changing the amount of CTAB. The largest external surface area and mesoporous volume were 191 m²/g and 0.17 cm³/g. Adsorption of mesitylene on the MOR zeolitic samples showed that only a small amount of adsorption could be found in the microporous mordenite, but a large amount of adsorption in hierarchical mordenite which presented the characteristics of typical IV isotherm indicating a mesoporous structure. Catalytic properties of the MOR zeolitic samples were investigated by benzylation reaction of mesitylene and benzyl chloride. Compared with the traditional microporous mordenite, the reaction conversion on the hierarchical mordenite increased ~7 times and the reaction apparent rate constant increased ~19 times. This property is due to the expansive external surface areas and mesopores volume in the hierarchical mordenite zeolite which can effectively improve accessibility of the bulky reactants to acid sites and mass transfer rate of big products, and greatly promote the catalytic efficiency of bulky molecules.