Use of amphiphilic triblock copolymers to direct the organization of polymerizing silica species has resulted in the preparation of well-ordered hexagonal mesoporous silica structures (SBA-15) with uniform pore sizes up to approximately 300 angstroms. The SBA-15 materials are synthesized in acidic media to produce highly ordered, two-dimensional hexagonal (space group p6mm) silica-block copolymer mesophases. Calcination at 500°C gives porous structures with unusually large interlattice d spacings of 74.5 to 320 angstroms between the (100) planes, pore sizes from 46 to 300 angstroms, pore volume fractions up to 0.85, and silica wall thicknesses of 31 to 64 angstroms. SBA-15 can be readily prepared over a wide range of uniform pore sizes and pore wall thicknesses at low temperature (35° to 80°C), using a variety of poly(alkylene oxide) triblock copolymers and by the addition of cosolvent organic molecules. The block copolymer species can be recovered for reuse by solvent extraction with ethanol or removed by heating at 140°C for 3 hours, in both cases, yielding a product that is thermally stable in boiling water.

Triblock copolymer syntheses of mesoporous silica with periodic 50 to 300 angstrom pores

A family of highly ordered mesoporous (20−300 A) silica structures have been synthesized by the use of commercially available nonionic alkyl poly(ethylene oxide) (PEO) oligomeric surfactants and poly(alkylene oxide) block copolymers in acid media. Periodic arrangements of mescoscopically ordered pores with cubic Im3m, cubic Pm3m (or others), 3-d hexagonal (P63/mmc), 2-d hexagonal (p6mm), and lamellar (Lα) symmetries have been prepared. Under acidic conditions at room temperature, the nonionic oligomeric surfactants frequently form cubic or 3-d hexagonal mesoporous silica structures, while the nonionic triblock copolymers tend to form hexagonal (p6mm) mesoporous silica structures. A cubic mesoporous silica structure (SBA-11) with Pm3m diffraction symmetry has been synthesized in the presence of C16H33(OCH2CH2)10OH (C16EO10) surfactant species, while a 3-d hexagonal (P63/mmc) mesoporous silica structure (SBA-12) results when C18EO10 is used. Surfactants with short EO segments tend to form lamellar mesost...

Nonionic Triblock and Star Diblock Copolymer and Oligomeric Surfactant Syntheses of Highly Ordered, Hydrothermally Stable, Mesoporous Silica Structures

It is possible to say that zeolites are the most widely used catalysts in industry They are crystalline microporous materials which have become extremely successful as catalysts for oil refining, petrochemistry, and organic synthesis in the production of fine and speciality chemicals, particularly when dealing with molecules having kinetic diameters below 10 A The reason for their success in catalysis is related to the following specific features of these materials:1 (1) They have very high surface area and adsorption capacity (2) The adsorption properties of the zeolites can be controlled, and they can be varied from hydrophobic to hydrophilic type materials (3) Active sites, such as acid sites for instance, can be generated in the framework and their strength and concentration can be tailored for a particular application (4) The sizes of their channels and cavities are in the range typical for many molecules of interest (5-12 A), and the strong electric fields2 existing in those micropores together with an electronic confinement of the guest molecules3 are responsible for a preactivation of the reactants (5) Their intricate channel structure allows the zeolites to present different types of shape selectivity, ie, product, reactant, and transition state, which can be used to direct a given catalytic reaction toward the desired product avoiding undesired side reactions (6) All of these properties of zeolites, which are of paramount importance in catalysis and make them attractive choices for the types of processes listed above, are ultimately dependent on the thermal and hydrothermal stability of these materials In the case of zeolites, they can be activated to produce very stable materials not just resistant to heat and steam but also to chemical attacks Avelino Corma Canos was born in Moncofar, Spain, in 1951 He studied chemistry at the Universidad de Valencia (1967−1973) and received his PhD at the Universidad Complutense de Madrid in 1976 He became director of the Instituto de Tecnologia Quimica (UPV-CSIC) at the Universidad Politecnica de Valencia in 1990 His current research field is zeolites as catalysts, covering aspects of synthesis, characterization and reactivity in acid−base and redox catalysis A Corma has written about 250 articles on these subjects in international journals, three books, and a number of reviews and book chapters He is a member of the Editorial Board of Zeolites, Catalysis Review Science and Engineering, Catalysis Letters, Applied Catalysis, Journal of Molecular Catalysis, Research Trends, CaTTech, and Journal of the Chemical Society, Chemical Communications A Corma is coauthor of 20 patents, five of them being for commercial applications He has been awarded with the Dupont Award on new materials (1995), and the Spanish National Award “Leonardo Torres Quevedo” on Technology Research (1996) 2373 Chem Rev 1997, 97, 2373−2419

From Microporous to Mesoporous Molecular-Sieve Materials and Their Use in Catalysis

This critical review will be of interest to the experts in porous solids (including catalysis), but also solid state chemists and physicists. It presents the state-of-the-art on hybrid porous solids, their advantages, their new routes of synthesis, the structural concepts useful for their ‘design’, aiming at reaching very large pores. Their dynamic properties and the possibility of predicting their structure are described. The large tunability of the pore size leads to unprecedented properties and applications. They concern adsorption of species, storage and delivery and the physical properties of the dense phases. (323 references)

Hybrid porous solids: past, present, future

Materials with nanoscopic dimensions not only have potential technological applications in areas such as device technology and drug delivery but also are of fundamental interest in that the properties of a material can change in this regime of transition between the bulk and molecular scales. In this article, a relatively new method for preparing nanomaterials, membrane-based synthesis, is reviewed. This method entails synthesis of the desired material within the pores of a nanoporous membrane. Because the membranes used contain cylindrical pores of uniform diameter, monodisperse nanocylinders of the desired material, whose dimensions can be carefully controlled, are obtained. This "template" method has been used to prepare polymers, metals, semiconductors, and other materials on a nanoscopic scale.

https://science.sciencemag.org/content/sci/266/5193/1961.full.pdf

Nanomaterials: a membrane-based synthetic approach.

A mixture of aromatic hydrocarbons, comprising ethylbenzene and at least one xylene, is treated to convert the ethylbenzene to compounds that may be removed from the aromatic hydrocarbon stream and to isomerize any xylenes present. The ethylbenzene conversion catalyst is one that is effective for ethylbenzene conversion with minimal xylene loss, e.g., a silica bound intermediate pore size zeolite that has been selectivated. The xylene isomerization catalyst is one which is effective to catalyze xylene isomerization. Each of the catalysts of this invention may contain one or more hydrogenation or dehydrogenation components.

Selective ethylbenzene conversion

A process useful in steam cracking is disclosed for selectively converting a feed comprising C4+ dienes and oxygenate to a product comprising increased C2+ monoolefins and para-xylene levels by contacting said feed under diolefin conversion conditions with a catalyst comprising a porous crystalline material having a Diffusion Parameter for 2,2-dimethylbutane of about 0.1-100 sec−1 when measured at a temperature of 120° C. and a 2,2-dimethylbutane pressure of 60 torr (8 kPa), a temperature of 430° C. and 0.5 WHSV.

Process for converting dienes and oxygenates to para-xylene and light olefins

A mixture of aromatic hydrocarbons, comprising ethylbenzene and at least one xylene, is isomerized using a two reactor system to convert the ethylbenzene to compounds that may be removed from the aromatic hydrocarbon stream and to produce a product stream wherein the para-xylene concentration is approximately equal to the equilibrium ratio of the para-isomer. The catalyst present in the first reactor is one that is effective for ethylbenzene conversion with minimal xylene loss when operated under suitable conversion conditions, e.g., a catalyst comprising silica bound ZSM-5 that has been selectivated by one or more silicon impregnations or that has been coke selectivated. The catalyst present in the second reactor is one which is effective to catalyze xylene isomerization when operated under suitable conditions. Each of the catalysts of this invention may contain one or more hydrogenation or dehydrogenation components.

Xylene isomerization on separate reactors

A ex situ selectivated catalytic molecular sieve for enhanced shape selective hydrocarbon conversions in which a catalytic molecular sieve is modified by being exposed to at least two selectivation sequences, each sequence including an impregnation of the molecular sieve with a selectivating agent and a subsequent calcination of the impregnated molecular sieve. The ex situ selectivation method is also described, including the use of aqueous carriers for the selecting agent. Also a method for in situ trim-selectivating the modified catalytic molecular sieve. Also, a method for moderate steaming of the selectivated molecular sieve. Also a method for in situ trim-selectivating the modified catalytic molecular sieve. Also described is the process for shape selective hydrocarbon conversion comprising contacting a hydrocarbon feedstream under conversion conditions with the selectivated molecular sieve.

Multiple impregnation technique for the preparation of ex situ selectivated zeolite catalysts

A process is provided for catalytic conversion of feedstock comprising aromatic compounds to product comprising aromatic compounds which differs from said feedstock. The catalyst required in the process comprises a crystalline material having the structure of MCM-58. Said crystalline material may have been treated with one or more monomeric or polymeric siloxane compounds which decompose to oxide or non-oxide ceramic or solid-state carbon species.

Jeffrey S. Beck

Papers

Selective ethylbenzene conversion

Process for converting dienes and oxygenates to para-xylene and light olefins

Xylene isomerization on separate reactors

Multiple impregnation technique for the preparation of ex situ selectivated zeolite catalysts

Catalytic conversion of aromatic compounds