Ordered M41S synthesis

MCM-50 consists of stacks of silica and surfactant layers. Obviously, no pores are formed upon removal of the surfactant layers. The silica layers contact each other resulting in a nonporous silica. It is noteworthy to mention that materials of M41S type were probably already synthesized by Sylvania Electric Products in 1971 [32], However, at that time the high ordering of the materials was not realized [33], M41S-type materials are synthesized under basic reaction conditions. Scientists from the University of Santa Barbara developed an alternative synthesis procedure under acidic conditions. They also used alkyltrimethyl ammonium as the surfactant. The porous silica materials obtained (e.g., hexagonal SBA-3 Santa BArbara [SBA]) had thicker pore walls but smaller pore diameters. Furthermore, they developed materials with novel pore topologies, e g., the cubic SBA-1 with spherical pores. 

Since the first synthesis of mesoporous M41S alumosilicates in 1992 [1,2] numerous systems of mesoporous materials have been reported. The principle method of these syntheses consists of the utilisation of lyotropic liquid crystals as supramolecular templates, which act as structure directing agents in order to mesostructure inorganic building units. 

In 1992, researchers of the Mobil Oil Company introduced a new concept in the synthesis of mesoporous materials. They used supramolecular arrays of surfactant molecules as templating agents in order to obtain mesostructured silicates or alumosilicates which retain after calcination an ordered arrangement of pores with diameters between 2 and 10 nm and a narrow pore size distribution comparable to that of zeolites. These materials called M41S phases give access to the regime of the mesopores which is very interesting for different kinds of new size selective applications, e.g., molecular sieves, catalysis and nanocomposites [1]. 

The synthesis of ordered mesoporous material was started as early as the 1970s. A research group in Japan also started synthesis work in 1990. Only the report of the M41S... 

The initial templates for the M41S family materials are quaternary ammonium surfactants with positive charge and long tail (hydrocarbon chain). The synthesis was believed to proceed via the formation of a lyotropic liquid crystal, which is an ordered assembly of micelles (details will be discussed in the mechanism section). The... 

The use of microporous solid catalysts such as zeolites and related molecular sieves has an additional benefit in organic synthesis. The highly precise organization and discrimination between molecules by molecular sieves endows them with shape-selective properties [12] reminiscent of enzyme catalysis. The scope of molecular sieve catalysis has been considerably extended by the discovery of ordered mesoporous materials of the M41S type by Mobil scientists [13,14]. Furthermore, the incorporation of transition metal ions and complexes into molecular sieves extends their catalytic scope to redox reactions and a variety of other transition metal-catalyzed processes [15,16]. 

Ordered Mesoporous Molecular Sieves (M41S Materials), 283 Synthesis Pathways for Ordered Mesoporous Materials, 284 Ordered Mesoporous Silica, 288 Fimetionalization of Mesoporous Materials, 296 Nonsdiceous Mesostructured and Mesoporous Materials, 302 Morphology, 309... 

Chapter 4 authored by /. C. Vartuli, W.. Roth, J. S. Beck, S.B. McCullen and C. T. Kresge is devoted to the synthesis and properties of zeolite-like amorphous materials of the M41S class with ordered mesopores. These mesoporous solids are currently being scrutinized in numerous laboratories for their potential as adsorbents and catalysts. 

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