Synthesis of mesoporous molecular sieves

ExxonMobil Research and Engineering Co., 1545 Route 22 East, Annandale, NJ 08801, USA. e-mail wieslaw.j.roth cxxonmobil.com 

DISCOVERY AND FUNDAMENTAL PROPERTIES OF THE M41S FAMILY OF MESOPOROUS MOLECULAR 

EXPLOITING SURFACTANT SYSTEM PHENOMENA IN THE SYNTHESIS OF MESOPOROUS MATERIALS 

SYNTHESIS OF MICRO- AND MHSO-POROUS HYBRID MATERIALS 

The title materials are synthesized in the presence of surfactants and were recognized first in the silica-cationic surfactant systems. The area expanded rapidly becoming an independent, though closely connected to zeolites, interdisciplinary field with potential of practical applications in catalysis and sorption. The discussion outlines the major advances in the synthesis of these materials from discovery to the present, stressing the general trends and interplay between surfactant and oxide chemistries. Representative materials are discussed in detail from the standpoint of convenient synthesis of a high quality useful product. 

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A fascinating area is micellar autocatalysis reactions in which surfactant micelles catalyse the reaction by which the surfactant itself is synthesized. Thus synthesis of dimethyldoceylamino oxide (reaction between dimethyl dodecyl amine and H2O2) benefits from this strategy. Here an aqueous phase can be used and an organic solvent can be avoided. Synthesis of mesoporous molecular sieves benefit through micellar catalysis and silicate polymerization rates have been increased by a factor 2000 in the presence of cetyltrimethyl ammonium chloride (Rathman, 1996). 

The review of Notari (33) covers the synthesis methodologies of titanium silicate molecular sieves available up to 1996. The reviews of Corma (279) and subsequently of Biz and Occelli (280) describe the synthesis of mesoporous molecular sieves. An informative article on the preparation of TS-1 was reported recently by Perego et al. (68). In this section we list some of the recent developments in the synthesis of micro and mesoporous titanosilicate molecular sieves. 

Reddy, K.M. and Song, C.S. Synthesis of mesoporous molecular sieves Influence of aluminum source on A1 incorporation in MCM-41. Catalysis Letters, 1996, 36, 103. 

J. C. Vartuli, C. T. Kresge, W. J. Roth, S. B. McCullen, J. S. Beck, K. D. Schmitt, M. E. Leonowicz, J. D. Lutner, E. W. Sheppard, Designed synthesis of mesoporous molecular sieve systems using surfactant directing agents, in W. R. Moser(Ed.), Advanced Catalysts and Nanostructured Materials Modern Synthetic Methods, Academic Press, San Diego, 1996, pp. 1-19. 

Effect of nature and precursors of metal ions, M/Si molar ratio, M1/M2 molar ratio and silica sources on the synthesis of mesoporous molecular sieves... 

Synthesis of organized mesoporous aluminas is based on the same approaches as those successfully used for the synthesis of mesoporous molecular sieves ( anionic , cationic , and neutral ) using aluminum alkoxide as the source of aluminum and in the absence of any silicon source. In contrast to the synthesis of siliceous MCM-41, the cationic route to organized mesoporous aluminas using hexadecyltrimethylammonium cations is the least applied and understood. Cabrera et al. [68] described the possibility to tailor the pore dimensions from 3.3 to 6.0 nm by modifying the ratio of surfactant, water and triethanolamine however, this synthesis route seems to be less reproducible compared with anionic and neutral routes. 

Synthesis of mesoporous molecular sieves MCM-41 and MCM-48 was carried out under microwave and hydrothermal conditions. Molecular sieves prepared were characterized using X-ray powder diffraction, scanning electron microscopy, nitrogen adsorption isotherms and infrared spectroscopy to evaluate the properties of these materials. It was observed that mesoporous molecular sieves synthesized under microwave conditions exhibit higher activity in oxidation of adamantanone by hydrogen peroxide to the respective lactone (Baeyer-Villiger oxidation). 

The influence of alkali/silica molar ratio in the synthesis of mesoporous molecular sieve materials was studied in a simple synthesis system containing tetraethylorthosilicate, water, alkali and the cetyltrimethylammonium bromide at room temperature. The resulting silicate materials were characterized by XRD, Si MAS NMR, TEM and N2 adsorption-desorption isotherms. The results suggest that the formation of different surfactant-silicate aggregation array morphology not only relies on an interaction between silicate ions and the surfactant, but also on a proportion of the silicate species to surfactant. 

P-24 - Synthesis of mesoporous molecular sieves MCM-48 under several reaction conditions... 

Other specific areas of micellar catalysis in which industry has expressed interest are in micellar phase-transfer catalysis and in the synthesis of mesoporous molecular sieves [92]. In the first example of the latter application, investigators at Mobil were able to control pore size and properties by synthesizing the desired mesoporous material in the presence of appropriately sized, structured, and charged micelles [96]. The burst of research activity in this area that occurred in the next few years after this discovery has been reviewed by Huo et al. [97]. 

Synthesis of mesoporous molecular sieves with amorphous channel walls of various chemical compositions. different pore sizes, and dimensionalities. 

Figure 1. Scheme of the synthesis of mesoporous molecular sieves using surfactant micelles as a structure-directing agent [1]. 

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