离子热合成沸石分子筛:技术特性、研究进展与应用前景

离子热法是一种以离子液体或低共熔物为反应介质、在低挥发性的离子态反应环境中合成沸石分子筛的方法。离子热合成可在接近常压下进行, 因此不但能够克服常规液相合成体系高压带来的操作困难, 而且为分子筛合成机理研究提供了便利, 同时便于与微波等电磁技术耦合。本文总结了离子热法在沸石分子筛材料合成及机理研究方面取得的进展。通过调变反应介质种类、反应物组成、晶化条件以及添加氟或有机胺等可以得到不同组成、结构的沸石分子筛产物以及AlPO、SAPO分子筛膜;在离子热合成过程中, 离子液体和低共熔物的阳离子、有机胺或铵盐、金属阳离子等能够独立或协同起到结构导向作用。预期离子热法可为分子筛器件的放大生产提供一条灵活、方便的途径。

Ionothermal synthesis of zeolitic molecular sieves:Properties,progress and prospect

Ionothermal synthesis is a method that uses either ionic liquid (IL) or deep eutectic solvent (DES) as reaction medium to synthesize zeolitic molecular sieves. The reaction environment of ionothermal synthesis is ionic and extremely low volatile. This is due to the inherent characteristics of IL/DES, as well as their isolation-deactivation effect on molecular reactants via hydrogen bonds. Compared with hydro/solvothermal routes, the most significant property of ionothermal synthesis is that it can take place at ambient pressure with few safety risks. This property brings convenience to in situ studies, and benefits the application of microwave heating to the synthesis of molecular sieves. Moreover, great flexibility is shown in ionothermal synthesis. By alternating reaction medium, reactant composition and crystallization condition, zeolitic products with various compositions and structures can be ionothermally synthesized. In the past decade, fruitful results have been obtained with respect to both the synthesis of zeolitic materials and the study of formation mechanisms of molecular sieves. Ionothermal synthesis has been proven as a promising method to prepare zeolitic phosphates. More than 20 zeolite framework types of zeolitic phosphates have been ionothermally synthesized until now. Some of these zeolitic phosphates, such as CoAPO-SIV and AlPO-CLO, have never been obtained from traditional systems. Under ionothermal conditions, a variety of zeolite films and membranes, such as AlPO, SAPO and metal-organic framework, have been prepared via the in situ method or the substrate surface conversion method. The substrate surface conversion method can be applied to preparing AlPO membranes on porous Al₂O₃, which is used as both substrate and aluminium source. This method inhibits the crystallization of molecular sieves in the liquid phase, avoids the influence of species diffusion on membrane formation, and benefits the formation of membranes with high quality. Under ionothermal conditions, various species, such as the cations of IL/DES, the additive amines/ammonium cations and the metal cations, have potential structure directing ability. The complex cations, which are formed by amine molecules and IL/DES cations via hydrogen bonds, can also play the role of structure directing agent. Compared with molecular solvents, IL and DES have little disturbance to the structure directing process during the formation of molecular sieves. Considering its fascinating features, ionothermal synthesis would be a rational choice for the industrial preparation of zeolite-based devices.