Crystalline mesoporous molecular sieves have long been sought as solid acid catalysts for organic reactions involving large molecules. We synthesized a series of mesoporous molecular sieves that possess crystalline microporous walls with zeolitelike frameworks, extending the application of zeolites to the mesoporous range of 2 to 50 nanometers. Hexagonally ordered or disordered mesopores are generated by surfactant aggregates, whereas multiple cationic moieties in the surfactant head groups direct the crystallization of microporous aluminosilicate frameworks. The wall thicknesses, framework topologies, and mesopore sizes can be controlled with different surfactants. The molecular sieves are highly active as catalysts for various acid-catalyzed reactions of bulky molecular substrates, compared with conventional zeolites and ordered mesoporous amorphous materials.

http://science.sciencemag.org/content/sci/333/6040/328.full.pdf

Directing Zeolite Structures into Hierarchically Nanoporous Architectures

The NH3-SCR activity of the small-pore zeolites, Cu-SSZ-13, Cu-SSZ-16, and Cu-SAPO-34, is investigated using a high-throughput reactor system. These copper exchanged small-pore zeolites have high SCR activity between 150 and 500 °C and are shown to be much more hydrothermally stable than the medium-pore zeolite, Cu-ZSM-5. The degree of copper exchange, the dimensionality of the framework, and heteroatom framework substitution all impact the SCR activity and hydrothermal stability of the materials. Of the small-pore zeolites tested, Cu-SSZ-13 and Cu-SAPO-34 display superior SCR performance, both before and after high-temperature hydrothermal treatment.

The ammonia selective catalytic reduction activity of copper-exchanged small-pore zeolites

The presence of basic centers in some oxides has been recognized for a long time as being important in catalysis [1-4]. Usually both basic and acid sites exist simultaneously. The two centers may work independently or in a concerted way. For instance, in alcohol transformation, dehydration is favored on acidic sites and dehydrogenation on basic centers [3,5]. A large variety of materials are cited as having basic character. They include single-metal oxides (MgO, CaO, ZnO), supported alkali metals (Na/MgO, K/K2CO3), mixed-metal oxides (MgO-A12O3, ZnO-SiO2, MgO-TiO2), zeolites (X and Y saturated with alkaline cations of low electronegativity), hydrotalcite-type anionic clays, asbestoslike materials, carbon-supported basic catalysts, and basic organic resins. ∗ Present address: 16 rue Francois Gillet, 69003 Lyon, France.

Basic zeolites : Characterization and uses in adsorption and catalysis

Characterization of nanocrystalline zeolite Beta

Incorporation of Ti into the framework of aluminium-free zeolite Beta has been achieved in F- medium and has produced hydrophobic selective oxidation catalysts. The Ti−Beta(F) materials have been characterized by X ray diffraction, infrared, Raman, ultraviolet, XANES, EXAFS, 29Si MAS NMR, and 1H→29Si CP MAS NMR spectroscopies, adsorption microcalorimetry, and catalytic testing. At near neutral pH the incorporation of Ti into the framework appears to present an upper limit of ca. 2.3 Ti/uc, beyond which anatase is detected in the calcined materials. However, at higher pH (ca. 11) larger amounts of Ti can be incorporated without anatase formation. After calcination, Ti incorporation in the framework is characterized by an increase in the unit cell volume, the appearance of one Raman band and three infrared bands in the region near 960 cm-1 and the presence of a strong absorption band in the 205−220 nm ultraviolet spectrum. By 29Si MAS NMR, 1H→29Si CP MAS NMR, and infrared spectroscopies it is concluded that...

Direct Synthesis and Characterization of Hydrophobic Aluminum-Free Ti−Beta Zeolite

The framework topology of zeolite beta

The tetrahedral framework structure of zeolite beta is disordered along (001). The disordered structure is related by a/3 and/or b/3 displacements on (001) planes to three ordered polytype structures with triclinic, monoclinic, and tetragonal symmetry. Three mutually perpendicular 12-ring channel systems are characteristic of the three ordered polytypes and the disordered beta structure. The proposed framework structures are consistent with the known diffraction, sorption an cation exchange properties of zeolite beta.

G.T. Kerr

Papers

The framework topology of zeolite beta

The framework topology of zeolite beta

Aluminum incorporation into high silica zeolites

Exchange of tetraethylammonium ion into zeolite Y

The framework topology of zeolite beta — a correction