Supramolecular Host‐Guest Systems in Zeolites Prepared by Ship‐in‐a‐Bottle Synthesis

Zeolite Mediated Reactions: Mechanistic Aspects and Environmental Applications

An overview is presented of basic research and applications for the use of zeolites in environmentally-related topics. The use of these materials to promote oxidation reactions, and other catalytic processes is surveyed along with ship-in-a-bottle synthesis of particular zeolite-encapsulated catalysts. Methods for probing the surfaces of zeolites using spin-probes and ESR detection are mentioned. The ability of some thermally activated zeolites to produce spontaneously radical cations by single-electron oxidation of organic molecules is reviewed. The issue of the degree of acidity of H-zeolites is discussed, which demonstrates them not to be super-acids. Some ESR determinations of the adsorption of NOx species onto selected zeolites are reviewed and the use of zeolites to catalyse desulfurisation of hydrocarbons is considered. Finally, there is mention made of the use of zeolites to catalyse hydrodechlorination of CFC's and other organic chlorine-containing compounds. Surfactant-modified zeolites (SMZ) for use as polyfunctional decontamination agents are further discussed. Theoretical methods, e.g. Density Functional Theory (DFT), are finding their own application to studying the mechanisms of reactions that are mediated by zeolites as is shown throughout.

Asymmetric reactions on chiral catalysts entrapped within a mesoporous cage

The encapsulation of homogeneous chiral catalysts, e.g. Co(Salen) and Ru-TsDPEN, in the mesoporous cage of SBA-16 is demonstrated; the encapsulated catalysts show performance as good as that of the homogeneous catalysts, and can be recycled for more than 10 times without significant loss of catalytic performance.

Encapsulation of Cu(II) Purine Derivative Complexes in NaY Zeolite

The encapsulation of Cu(II) purine derivative complex was carried out by ion exchange of the complex from aqueous solutions into zeolite NaY. The entrapped complex was characterized by spectroscopic methods (FTIR and ICP-AES) and surface analysis (XRD). The various techniques of characterization used show that the Cu(II) complex was effectively encapsulated in the zeolite and this process does not modify the morphology and structure of the NaY zeolite. These materials have potential applications in heterogeneous catalysis in mild reaction conditions.

Silver nitrate in silver zeolite A: three-dimensional incommensurate guest ordering in a zeolite framework

We report the results of a detailed examination of the occlusion of silver nitrate in silver zeolite A (AgA). The superlattice reported to occur in (AgNO3)9-AgA was found to melt at between 80 and 100 degrees C on heating and reappear when the sample was cooled down to 80 degrees C. Annealing in this temperature range and rigorous exclusion of water produced an enhancement of the superlattice peaks, which results from ordering of the contents of the zeolite cages. Peaks assigned to the superlattice were indexed with the tetragonal lattice parameters a = 17.440(5) and c = 12.398(4) A and proposed space group P4/nmm. The sharp peaks representing the lattice of the framework (a = 12.3711(5) A, Pm3m) remained largely unaffected by the guest in this compound, which was found to exhibit strong negative thermal expansion. The host and guest lattices are incommensurate with the tetragonal guest lattice being slightly larger than the cubic host in the c-direction and slightly smaller in the a- and b-directions.

Anchoring Dyes into Multidimensional Large-Pore Zeolites: A Prospective Use as Chromogenic Sensing Materials

A versatile procedure for anchoring dyes into the pores of multidimensional zeolites by including organic dye precursors in the synthesis gel has been developed. To prove the concept, an aniline-functionalised zeolite Beta was obtained by reaction of triethylorthosilicate (TEOS), tetraethylammonium hydroxide, and N-methyl,N-(propyl-3-trimethoxysilyl)aniline (MPTMSA) in the presence of HF. Further extraction of the structure-directing agents resulted in a highly crystalline, white, functionalised zeolite Beta containing anchored aniline groups. Similar organic functionalised molecular sieves (OFMS) have been explored as novel catalysts, but, as far as we know, OFMS have never been used as precursors for dye-immobilisation or to design new solid-based host systems for selective molecular sensing processes as is reported here. In a second step the solids containing dyes were prepared by reaction of the hybrid material with the appropriate reactives to obtain tricyanovinylbenzene, triphenylpyrylium, azoic, and squaraine derivatives. All these reactions are straightforward and involve electrophilic aromatic substitution or diazotisation reactions at the electron-rich aniline ring. The final dye-functionalised solid materials were isolated by simple filtration and washing procedures and have been characterised by a number of techniques. In all cases the Beta structure of the solid remains unaltered. Among the large number of areas where dye-containing zeolites might be of importance, we were interested in testing their unconventional use as heterosupramolecular hosts in chromogenic protocols. To check their potential use as chemosensors, microporous solids with anchored triphenylpyrilium and squaraine dyes were selected and used as sensors for the chromogenic discrimination of amines. It was found that the response of both solids to amines was basically governed by the three-dimensional (3D) solid architecture that tuned the intrinsic unselective reactivity of the pyrylium dye. By using new solid-state supramolecular chemistry protocols we believe that these, and similar future dye-zeolite hosts, might be promising new sensor materials allowing the visible discrimination of selected target guests by size and/or polarity within families or closely related molecules.

Synthesis and Luminescence Properties of Ag2S and PbS Clusters in Zeolite A

Zeolite A provides a suitable environment to host Ag2S and PbS clusters, so that spectroscopic investigations on very small particles are possible. The Ag2S monomer is colorless and shows photoluminescence at 490 nm with a lifetime of 300 micros, while the absorption and luminescence of Ag4S2 and larger clusters are red-shifted. The properties of these Ag2S/zeolite A materials depend on the co-cations. Results for Li+, Na+, K+, Rb+, Cs+, Mg2+, Ca2+, and Sr2+ are reported. Excitation energy transfer between Ag2S and Ag4S2 has been studied in materials containing Ca2+ co-cations. PbS particles can be prepared by the same method as Ag2S in the cavities of zeolite A. The PbS monomers obtained are yellow and show photoluminescence at 570 nm, with a lifetime of 700 ns.