Water-tolerant solid acid catalysts.

Zeolites have proved to be valuable technical catalysts in petrochemistry and in oil processing. The characteristic properties of zeolites, such as acidity, shape-selectivity and thermal stability also enable them to be used for highly selective synthesis in the fields of chemical intermediates and fine chemicals. This interesting area of application has grown continuously in recent years. The present article summarizes the various standard types of reaction involved in organic syntheses which can be catalyzed by zeolites; these include, inter alia, electrophilic and nucleophilic substitution reactions, isomerization of double bonds and carbon skeletons, as well as addition, elimination and hydrogenation reactions.

Zeolites: Catalysts for Organic Syntheses

The change in shape inducible in some photo-reversible molecules using light can effect powerful changes to a variety of properties of a host material. This class of reversible light-switchable molecules includes molecules that photo-dimerize, such as coumarins and anthracenes; those that allow intra-molecular photo-induced bond formation, such as fulgides, spiro-pyrans, and diarylethenes; and those that exhibit photo-isomerization, such as stilbenes, crowded alkenes, and azobenzenes. The most ubiquitous natural molecule for reversible shape change, however, and perhaps the inspiration for all artificial bio-mimics, is the rhodopsin/retinal protein system that enables vision, and this is the quintessential reversible photo-switch for performance and robustness. Here, the small retinal molecule embedded in a cage of rhodopsin helices isomerizes from a cis geometry to a trans geometry around a C=C double bond with the absorption of just a single photon. The modest shape change of just a few angstroms is quickly amplified and sets off a cascade of larger shape and chemical changes, eventually culminating in an electrical signal to the brain of a vision event, the energy of the input photon amplified many thousands of times in the process. Complicated biochemical pathways then revert the trans isomer back to cis, and set the system back up for another cascade upon subsequent absorption. The reversibility is complete, and many subsequent cycles are possible. The reversion mechanism back to the initial cis state is complex and enzymatic, hence direct application of the retinal/rhodopsin photo-switch to engineering systems is difficult. Perhaps the best artificial mimic of this strong photo-switching effect however in terms of reversibility, speed, and simplicity of incorporation, is azobenzene. Trans and cis states can be switched in microseconds with low-power light, reversibility of 105 and 106 cycles is routine before chemical fatigue, and a wide variety of molecular architectures is available to the synthetic materials chemist, permitting facile anchoring and compatibility, as well as chemical and physical amplification of the simple geometric change. This review article focuses on photo-mechanical effect taking place in various material systems incorporating azobenzene. The photo-mechanical effect can be defined as reversible change in shape by absorption of light, which results in a significant macroscopic mechanical deformation, and reversible mechanical actuation, of the host material. Thus, we exclude simple thermal expansion effects, reversible but non-mechanical photo-switching or photo-chemistry, as well as the wide range of optical and electro-optical switching effects for which good reviews exist elsewhere. Azobenzene-based material systems are also of great interest for light energy harvesting applications across much of the solar spectrum, yet this emerging field is still in an early enough stage of research output as to not yet warrant review, but we hope that some of the ideas put forward here toward promising future directions of research, will help guide the field.

Azobenzene photomechanics: prospects and potential applications

https://repository.tudelft.nl/islandora/object/uuid%3A78157776-3f56-4e01-bb61-acfcd40c7279/datastream/OBJ/download

High-silica zeolites for adsorption of organic micro-pollutants in water treatment: A review.

https://ris.utwente.nl/ws/files/6882341/zeolite_1.pdf

Zeolite-filled silicone rubber membranes : Part 1. Membrane preparation and pervaporation results

Hydrophobic natures of zeolite ZSM-5

Crystallization rates of ZSM-5 from the reaction mixture of TPA single cation system was measured in relation with the composition of the reactants The crystallization rate strongly depended on concentration ratios of the components such as (TPA)2O/SiO2, SiO2/Al2O3 and H2O/SiO2 ie, it increased along with increasing (TPA)2O/SiO2 and SiO2/Al2O3 and decreased with increasing H2O/SiO2 Na cation did not seem to play a major role in the crystallization from the Na-TPA cation system with SiO2/Al2O3 ratio above ca 100

Crystallization of zeolite ZSM-5 from single cation system.

The removal of aluminium cations from Y type zeolite, faujasite, was studied by means of three methods of treatment, i.e., acetic acid–sodium acetate buffer treatment, acetate buffer–Na2H2EDTA treatment and H4EDTA treatment. It was confirmed from the results that the reagent for dealumination of faujasite should have two functions, i.e. weakly acidic and chelating ability with aluminium cations. When more than 23 aluminium cations were extracted from 53 aluminium atoms in a unit cell, lattice was seriously destroyed. But the analysis of the adsorption isotherms suggested that more than 66% of α-cages remained even in a nearly amorphous sample obtained after dealumination as far as 75%. The differential heat of immersion of the dealuminated Y type zeolite in water showed that the acid strength of the surface increased slightly by dealumination.

Preparation and Properties of Dealuminated Y Type Zeolite

Zeolite ZSM-5 was synthesized as the only crystalline phase from Na-Amido cation system for the first time. An isothermal metastable phase transformation diagram was described for Na-OEL cation system. OEL cation facilitated crystallization of ZSM-5 better rather than TPA one.

Crystallization of zeolite ZSM-5 in the Na-amido cation system.

A method of synthesizing a crystalline aluminosilicate zeolite from a reaction mixture containing a base, silica, alumina and water, wherein an alkali metal compound and an amide compound are concurrently used as said base.

Hiromi Nakamoto

Papers

Hydrophobic natures of zeolite ZSM-5

Crystallization of zeolite ZSM-5 from single cation system.

Preparation and Properties of Dealuminated Y Type Zeolite

Crystallization of zeolite ZSM-5 in the Na-amido cation system.

Method of preparing crystalline aluminosilicate zeolites