Microwave assisted zeolite synthesis

The use of ionic hquids (ILs) or eutectic mixtures as solvent in zeolite synthesis has been reported [178]. The IL, viz. l-methyl-3-ethylimidazolium bromide, was used both as solvent and as SDA. It solubilizes all components involved in the synthesis, while the electrostatic interaction between cations, IL and framework species form the basis of a strong templating effect [165, 178]. It was shown that the IL also works as a microwave absorber [172] and is suited for microwave-assisted zeolite synthesis. Because of the low vapor pressure of IL, the synthesis occurs at low pressure. The addition of amines to such synthesis mixtures yields pure API and ATV structures. The amine as well as the IL seem to exert a structure-directing effect [179]. This method is particularly useful for preparation of transition-metal functionalized frameworks, viz. Co-AlP04-n [180]. New zeotypes were obtained in the Al, P system, viz. SIZ-7, as well as in the Si system, viz. SIZ-12. 

Inada, M., Tsujimoto, H., Eguchi, Y., Enomoto, N., Hojo, J. Microwave-assisted zeolite synthesis from coal fly ash in hydrothermal Process. Fuel 84, 1482-1486 (2005)... 

O. Muraza, E.V. Rebrov, J. Chen, M. Putkonen, L. Niinisto, M.H.J.M. de Croon, J.C. Schouten, Microwave-assisted hydrothermal synthesis of zeolite Beta coatings on ALD-modified borosilicate glass for application in microstructured reactors, Chem. Eng. J. 135 (2008) SI 17. 

In order to accelerate the synthesis of both zeolite seeds and membranes, microwave-assisted hydrothermal synthesis (MW-HT) revealed an attractive method. Colloidal zeolite seeds can be successfully prepared by MW-HT synthesis [100,112,113]. Starting from a seeded support,... 

Bux H, Liang EY, Li YS et al (2009) Zeolitic imidazolate framework membrane with molecular sieving properties by microwave-assisted solvothermal synthesis. J Am Chem Soc 131 16000... 

Importantly, ionic liquids show excellent properties on the adsorption of microwave. The combination of microwave-assisted synthesis and ionothermal synthesis opens up an efficient and safe route to prepare zeolite materials [60]. Tian and coworkers reported the microwave-assisted ionothermal synthesis of AlPO-ll using [EmimJBr [61]. Silicon element was also successfully introduced to the framework forming SAPO-11 with potential catalytic applications. In addition, Yan and coworkers developed the ambient pressure synthesis method for silicate zeolites by combining the advantages of ionothermal synthesis, dry-gel conversion, and microwave irradiation [62]. With the assistance of microwave-assisted synthesis, the safe and fast process of ionothermal synthesis has shown to be a promising synthetic route for a variety of zeolite structures. 

Supported zeolite membranes have been prepared using numerous procedures [4] such as alignment of crystals in electrical fields, electroplating, self-assembly, growth on organic molecular layers, covalent linkages, hydrothermal synthesis (in situ and ex situ), hydrothermal method microwave heating assisted, dry gel method (vapor-phase transport method and steam-assisted crystallization), synthesis at the interface between two fluid phases, etc. 

A one-pot synthesis of N-substituted 4-aryl-l, 4-dihydropyridines using a microwave-assisted procedure was described in 2001 (Scheme 10.97) [187]. Among a variety of solid supports (Kio, acidic alumina, zeolite HY, silica gel), silica gel was proved to be the most efficient. After irradiation for 4 min, the reactions led to yields ranging from 62 to 94%. 

Recently, Yu and coworkers have successfully controlled the crystal size and morphology of the silicoaluminophosphate zeolite SAPO-34 (CHA) under microwave irradiation in the system of AljOj-P Oj-SiOj-TBAOH-H O by studying the synthetic factors such as the silica source, water content, crystallization time, and aging time [52]. Microwave-assisted synthesis proved to be an efficient approach to produce nanosized zeolite crystals [53]. As a comparison to traditional hydrothermal synthesis at 200°C for 72 h, the microwave-assisted synthesis of SAPO-34 needed only 1 h at 200°C, which greatly reduced the reaction time. 

Tanaka, H., Fujii, A., Pujimoto, S., Tanaka, Y. Microwave-assisted two-step process for the synthesis of a single-phase Na-A zeolite from eoal fly ash. Adv. Powder Technol. 19, 83-94 (2008)... 

Xu X, Bao Y, Song C, Yang W, Lin J and Lin L (2004), Microwave-assisted hydro-thermal synthesis of hydroxy-sodahte zeolite membrane , Micropor Mesopor Mafer, 75,173-181. 

In a word, ion-exchange with the assistance of microwaves is feasible, convenient, and fast. It can reach a higher exchange degree than can traditional methods and make the inaccessible ions in traditional methods exchangeable. This method is especially appropriate for the laboratory preparation of ion-exchanged zeolite molecular sieves. The microwave technique is very successful in the synthesis of microporous crystals, modification of the properties of zeolites, secondary synthesis of microporous materials, and the preparation of ultra-fine particles and films, and has attracted the wide interest of chemists in the field of molecular sieves. 

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