Dry gel conversion

TS-l/MCM-41 catalysts synttiesized by the dry gel conversion method are shown to have hexagonal mesopores. The catalytic activity of synthesized TS-l/MCM-41 catalysts was tested with qroxidation reaction of olefins to reved that both the conversion of olefins and selectivity to epoxide are higher than those of H-MCM-41,... 

In this work, highly active epoxidation catalysts, which have hydrophobic surface of TS-1, were synthesized by the dry gel conversion (DGC) method. Ti-MCM-41 was synthesized first by a modifed method and the TS-l/MCM-41 catalysts were subsequently synthesized by the DGC method. The catalysts were characterized by the XRD, BET, FT-IR, and UV-VIS spectroscopy. TS-l/MCM-41 catalysts were applied to the epoxidation of 1-hexene and cyclohexene with aqueous H202to evaluate their activities for the epoxidation reaction. ... 

Titanium containing hexagonal mesoporous materials were synthesized by the modified hydrothermal synthesis method. The synthesized Ti-MCM-41 has hi y ordered hexa rud structure. Ti-MCM-41 was transformed into TS-l/MCM-41 by using the dry gel conversion process. For the synthesis of Ti-MCM-41 with TS-1(TS-1/MCM-41) structure TPAOH was used as the template. The synthesized TS-l/MCM-41 has hexagonal mesopores when the DGC process was carried out for less than 3 6 h. The catalytic activity of synthesized TS-l/MCM-41 catalysts was measured by the epoxidation of 1-hexene and cyclohexene. For the comparison of the catalytic activity, TS-1 and Ti-MCM-41 samples were also applied to the epoxidation reaction under the same reaction conditions. Both the conversion of olefins and selectivity to epoxide over TS-l/MCM-41 are found hi er flian those of other catalysts. 

In 1990, Xu et al. first reported the transformation of a dry aluminosilicate gel to crystalline MFI by contact with vapors of water and volatile amines, which was named dry gel conversion (DGC).[99] Since then, this method has been extensively studied and a large number of microporous materials with new compositions and structures were prepared. Generally, DGC can be divided into vapor-phase transport (VPT) and steam-assisted conversion (SAC) according to the volatility of the SDAs. For volatile SDAs such as ethylenediamine, a mixture of water and SDA was poured into the bottom of the autoclave and then a dry gel, which does not contain any SDAs, was placed over the liquid surface. Water and SDAs were vaporized at elevated temperature (150 200 °C), reached the dry gel, and initiated the crystallization, which was called VPT. Less volatile SDAs such as tetrapropylammonium hydroxide were usually involved in the dry gel. Only water steam is supplied during the reaction, which was called SAC. 

Over the past 10 years, more crystallization systems supporting the solid-phase mechanism have been reported. Remarkable examples included Tsapatsis s study on the crystallization of zeolite L by using High Resolution Transmission Electron Microscope (HRTEM) technique in 1996 [23] Serrano s study on the crystallization of TS-1 by using a couple of spectral techniques in 1996[24] and on the crystallization of pure silica zeolite beta under the presence of F [25] and Uguina s study on the crystallization of TS-2 by using multiple techniques.[26] The commonly used dry-gel synthesis of zeolites in recent years (DGC and SAC, see Section 3.2.5, Sub-section Dry Gel Conversion in Chapter 3) partially confirms the rationality of the solid-phase mechanism. 

P-10 - Utilization of dry-gel conversion method for the synthesis of gallosilicate zeolites beta, ZSM-5 and ZSM-12... 

Synthesis of gallosilicate zeolites [Ga]-beta, [Ga]-ZSM-5 and [Ga]-ZSM-12 was performed by dry-gel conversion (DGC) method. The crystallization of the dry gel was performed in presence of small amount of water, without which the crystallization failed. The method was convenient and as effective as conventional hydrothermal method. The samples were pure and highly crystalline, and showed characteristic of typical gallosilicate zeolites. 

I S/WS hydrothermal synthesis nith seed HTSAVOS hych-odiermal synthesis without seed DGC dry gel conversion. 

HTS, hydrothermal synthesis in alkah media DGC, dry gel conversion PS, post-synthesis ... 

There are various routes of hydrothermal crystallisation such as the ionothermal synthetic route, micro-emulsion-based hydrothermal route, dry gel conversion synthetic route, solvo-thermal S5mthetic route and so forth, which can be studied. 

In a slightly different setup, which makes use of the so-called dry gel conversion, Zhang et al. [29] investigated conditions under which the silicoalu-minophosphate SAPO-34 is formed. However, this system seems to be more limited in scope, since only a fraction of the known crystalline microporous materials is accessible via the dry gel conversion route. Another special synthesis procedure was developed by the group of Gavalas, who describe the parallel synthesis of zeolite films [30]. The synthesis mixtures are formed in each well of a 21-well setup, then the substrate is placed on top of each well and the system turned around to expose the substrate to the synthesis mixture. Also in this case, product identification proceeds via XRD. Ideally, a microdiflf actometer should be used for analysis as the authors point out, but due to the unavailability of such a system, analysis was performed by conventional X-ray diffraction, covering all but one sample by lead foil. 

There are basically two approaches to synthesize supported zeolite membranes liquid-phase synthesis and vapor-phase transport (or dry-gel conversion) methods [2,12], The liquid-phase-synthesis approach is to bring the surface of a porous support in contact with a zeolite synthesis solution (sol or gel) and keep the system under controlled conditions so that the zeolite can nucleate and grow to a continuous film on the support surface. 

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. 

Cai R, Liu Y Gu S, Yan Y. Ambient pressure dry-gel conversion method for zeohte MFI synthesis using ionic liquid and microwave heating. J Am Chem Soc 2010 132 12776-7. 

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