Bound zeolites

More recently, using the same methodology as described above, a commercially available alumina-bound zeolite Beta (80 wt %) was tested for ethylbenzene synthesis (28). A first-order rate constant of 0.29 cm /g-sec was obtained. A 16% zeolite Beta in TUD-1 catalyst also had a rate constant of 0.30 cm ... 

This approach is commonly employed for bound zeolites. In this manner the relative amount of crystalline zeolite present can be determined. As usually implemented, the method provides a number that is the ratio of intensities for peaks in the diffraction pattern of the sample of interest to the intensity of the same peaks in the pattern of a reference zeolite. Since the intensity ratio is often expressed as a percentage, it is commonly referred to as percent zeolite crystallinity. The better terminology is relative amount of crystalline zeolite compared to a specific reference. 

Kulprathipanja, S. (1981) Cellulose acetate butyrate bound zeolite adsorbents. U.S. Patent 4,295,994. 

The alumina-bound zeolite samples were provided by Zeolyst Co. in extrudated form. The parent ZSM-5 samples had SiO 2/A1203 ratios of 30, 80 and 280, respectively. The parent Y zeolite samples had SiO 2/A1203 of 5, 30 and 80. The alumina binder was 20% by weight for all of the samples. Before testing, all of the samples were ground into powder and calcined at 560°C for 8 hours. 

The total acidities of both alumina-bound Y and ZSM-5 are increased compared with the parent zeolites. However, the total acidity for alumina-bound Y zeolite has a little bit more enhancement than alumina-bound ZSM-5 (Fig.l). For alumina-bound zeolite Y, the total acidity does not seem to change with Si02/Al203 ratio of the parent zeolite Y, while it seems to change slightly for alumina-bound ZSM-5. 

The total acidity of silica-bound zeolite samples is reduced compared with the theimnbound counterparts, especially for Y zeolite. The total acidity of silica-bound ZSM-5 zeolite samples is not reduced much. Fig. 7 shows the changes. 

Lewis acidity is greatly reduced both for the silica-bound Y and ZSM-5 at Si02/Al203 ratio, as shown in Fig.9. As Si02/Al203 ratio increases, the difference in Lewis acidities between bound zeolites and unbound zeolites is greatly reduced. 

Some Information on self-bound zeolites has been published.(S) Howell and Acara (6) have converted preformed aggregates of reactive kaolin-type clay, under appropriate conditions, directly to a zeolltlc phase. Metakaolln having a S1/A1 ratio of 1.0 was easily converted to zeolite A. Also,... 

Zeolites have much more open aluminosilicate frameworks than feldspars and this enables them to take up loosely bound water or other small molecules in their structure. Indeed, the name zeolite was coined by the mineralogist... 

Chemical and electrochemical techniques have been applied for the dimensionally controlled fabrication of a wide variety of materials, such as metals, semiconductors, and conductive polymers, within glass, oxide, and polymer matrices (e.g., [135-137]). Topologically complex structures like zeolites have been used also as 3D matrices [138, 139]. Quantum dots/wires of metals and semiconductors can be grown electrochemically in matrices bound on an electrode surface or being modified electrodes themselves. In these processes, the chemical stability of the template in the working environment, its electronic properties, the uniformity and minimal diameter of the pores, and the pore density are critical factors. Typical templates used in electrochemical synthesis are as follows ... 

Important metallic ore deposits include Besshi (Kieslager)-type (strata-bound cupriferous pyritic deposits), strata-bound Mn-Fe-type, skam-type, Kuroko-type and vein-type. Dominant non-metallic deposits are limestone, clay, native sulfur, zeolite, silica and gypsum deposits. The deposits are divisible into three groups, based on their ages of formation Carboniferous-Jurassic, Cretaceous-Paleogene and Tertiary-present. 

Chemically bound water, or water of crystallization, is divided into two main categories, bound water and zeolite water. They are distinguished by the effect upon... 

Operando DRIFTS examination of the working zeolite catalysts shows adsorbed hexane but do not support the presence of bound alkoxide/olefin/carbenium ion species. Data substantiate that alkanes may be activated without full transfer of zeolite proton to the alkane, i.e., without generation of any kind of real carbocation as transition state or surface intermediate. 

Zeolite-bentonite hybrid catalysts have been prepared from ZSM-5 and Beta zeolites supplied by Zeolyst International and bentonite. The zeolite to bentonite ratio was 35/65. The Si02 to A1203 ratio of ZSM-5 and Beta was 23 and 25, respectively. The preparation of the material was conducted in the following way. The zeolite and the bentonite were bound together through mixing in a 6 1 aqueous solution at 60°C for 2h,... 

By batch description trials Organo- and inorganically- modified zealot was subjected up to 24 hr in distilled water, tap water and 2% Nalco aqueous solutions in laboratory shaken machine to demonstrate how strongly the examined oxyanions are bound on the modified zeolite. While only slightly chromate desorption in the maximum extent about 20 mg/L was observed, approximately one order higher arsenate desorption was found, corresponding to increased ionic strength in waters. However, in both cases ODA-clinoptilolite exhibited the lowest desorption characteristics. Here, the... 

Not all quantum chemical calculations on zeolite clusters involve necessarily millions of integrations, and in the case of iso-electronic chemical systems fulfilling certain geometrical criteria, almost trivial back-of-an-envelope type calculations can yield rigorous upper and lower energy bounds. Fortunately, some zeolite structural units fulfill these geometric criteria. 

For zeolite structural units of the above size detailed ab initio calculations are prohibitively expensive even with the currently available most advanced computer programs. Convexity relation (13), and the resulting energy bounds, on the other hand, are easily applicable to a variety of similar problems, and require only few elementary algebraic operations. 

The currently available quantum chemical computational methods and computer programs have not been utilized to their potential in elucidating the electronic origin of zeolite properties. As more and more physico-chemical methods are used successfully for the description and characterization of zeolites, (e.g. (42-45)), more questions will also arise where computational quantum chemistry may have a useful contribution towards the answer, e.g. in connection with combined approaches where zeolites and metal-metal bonded systems (e.g. (46,47)) are used in combination. The spectacular recent and projected future improvements in computer technology are bound to enlarge the scope of quantum chemical studies on zeolites. Detailed studies on optimum intercavity locations for a variety of molecules, and calculations on conformation analysis and reaction mechanism in zeolite cavities are among the promises what an extrapolation of current developments in computational quantum chemistry and computer technology holds out for zeolite chemistry. 

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