Host−Guest Interactions in Pure-Silica and Aluminosilicate Sodalites Containing Ethylene Glycol as a Guest Molecule

Structural Features, Chemical Diversity, and Physical Properties of Microporous Sodalite-Type Materials: A Review

This review contains data on a wide class of microporous materials with frameworks belonging to the sodalite topological type. Various methods for the synthesis of these materials, their structural and crystal chemical features, as well as physical and chemical properties are discussed. Specific properties of sodalite-related materials make it possible to consider they as thermally stable ionic conductors, catalysts and catalyst carriers, sorbents, ion exchangers for water purification, matrices for the immobilization of radionuclides and heavy metals, hydrogen and methane storage, and stabilization of chromophores and phosphors. It has been shown that the diversity of properties of sodalite-type materials is associated with the chemical diversity of their frameworks and extra-framework components, as well as with the high elasticity of the framework.

Defect-stabilized nickel on beta zeolite as a promising catalyst for dry reforming of methane

Four different Ni-containing beta zeolite (Ni-BEA) catalysts were synthesized and applied for dry reforming of methane (DRM). Ni-BEA(I) exhibiting a nickel silicate was synthesized via the single-step interzeolite transformation of...

Conformation of intrazeolitic choline ions and the framework topology of zeolite hosts

A close relationship between the conformation of choline and the structure type of zeolites crystallized using this organic species was found.

The host–guest interactions in as-made zeolites Y, UZM-4, UZM-22, offretite, ferrierite, phillipsite, EU-12 and levyne, all of which were synthesized using choline as an organic structure-directing agent, have been investigated by a combination of different experimental techniques, including Raman, ¹H-¹³C CP MAS NMR and variable-temperature IR spectroscopies, together with theoretical calculations. The conformation of this asymmetric quaternary ammonium cation was shown to differ significantly according to the pore topology of the zeolite host and the intrazeolitic location of the organic guest molecule. Theoretical calculations using the pure-silica zeolite model reveal that among its three representative conformers (i.e., gauche, trans and trans′ forms), the conformer, which was experimentally found to dominantly or exclusively exist in zeolite structures studied, always has a lower interaction energy with the surrounding zeolite framework. Our work provides the first example in which the conformation of organic structure-directing agents plays an important kinetic role in governing the phase selectivity during zeolite nucleation.

Synthesis of aluminosilicate and gallosilicate zeolites via a charge density mismatch approach and their characterization

Aluminosilicate and gallosilicate zeolite syntheses via a charge density mismatch (CDM) approach are compared at intermediate-silica compositions (Si/Me = 5-16, where Me is Al or Ga). With a variation of the crystallization temperature and of the type and/or concentration of alkali metal ions added as a crystallization structure-directing agent (SDA) to tetraethylammonium-tetramethylammonium, tetraethylammonium-hexamethonium, and strontium-choline mixed-SDA systems, we were able to obtain 11 different zeolite structures. However, only 5 out of a total 40 pairs of aluminosilicate and gallosilicate synthesis runs at otherwise identical chemical compositions were found to give the same zeolite product with no detectable impurities, suggesting that the structure-directing ability of Ga is quite different from that of Al even in intermediate-silica synthesis conditions. The CDM approach to offretite synthesis led to hexagonal plate-like crystals with aspect ratios lower than 0.3, and UZM-22 exhibited no significant preference of Al substitution for particular tetrahedral sites, especially for site T1, unlike its framework type material ZSM-18. More interestingly, the EU-1 zeolite obtained from an aluminosilicate synthesis mixture containing Li(+) as an inorganic crystallization SDA in the tetraethylammonium-hexamethonium double-organic additive system has been characterized to locate about half of its Li(+) ions in the framework, while the Li distribution over the 10 topologically different tetrahedral sites is nonrandom in nature.

Synthesis and in situ transformation of PST-1: a potassium gallosilicate natrolite with a high Ga content

The synthetic details of a novel potassium gallosilicate natrolite with Si/Ga = 1.28, denoted PST-1, are described. The presence of K(+) and Ga with well-defined levels of concentration in the synthesis mixture is essential for directing its crystallisation. PST-1 transforms rapidly into TNU-6 under hydrothermal conditions, behaviour that contrasts sharply with its very high thermal and hydrothermal stability, which is unusual for a material of such a high Ga content. These stability issues are discussed and rationalized based on chemical composition, likely violations of Loewenstein's rule and the temperature of dehydration of as-made K-PST-1. The crystal structure of TNU-6 has been resolved through the combined use of synchrotron X-ray and electron diffraction data; it has the BaFeGaO(4) structure type with an additional radical 3a x radical 3a "GeAlO(4)" superstructure that arises from tilting of some of the tetrahedral units in all of the 6-rings.

A conformational study of 1-bromo-2-chloroethane in zeolites

The conformational properties of 1-bromo-2-chloroethane (BCE) in several representative zeolites including silicalite-1, siliceous Y (Si-Y), Na-Y, and zeolite L have been investigated by FT-Raman spectroscopy in combination with thermogravimetric analysis. The results indicate that the conformational and dynamic behavior of BCE inside a zeoltic host is strongly influenced by several factors such as the framework topology, the Si/Al ratio, and the nature and the locations of charge-balancing cations. For siliceous zeolites (silicalite-1 and Si-Y), the anti population of BCE increases significantly relative to pure liquid upon initial loading at room temperature. Interestingly, when lowering temperature, the anti population of BCE in silicalite-1 continues to increase, but the conformational equilibrium of BCE inside Si-Y shifts to the gauche conformer. Zeolite L and Na-Y with extra-framework cations show an almost exclusive preference for the gauche mode of the BCE molecule at room temperature, and the conformational population does not change significantly at low temperatures.

Molecular Conformations of Protonated Dipropylamine in AlPO4-11, AlPO4-31, SAPO-34, and AlPO4-41 Molecular Sieves

The host-guest interactions in AlPO4-11, AlPO4-31, SAPO-34, and AlPO4-41 molecular sieves prepared using the same organic structure-directing agent, i.e., dipropylamine, are investigated by a combination of Raman, 13C and 1H MAS NMR, and computer modeling studies. It was found that the organic molecules trapped within the pores of these four AlPO4-based materials exist as their protonated form and adopt distinct conformations in order to fit well with the pore structure of each host. In particular, the presence of two different types of conformations of protonated dipropylamine in the circular 12-ring channels of AlPO4-31 has been ascertained.