Crystallization zeolites

Soluble species -f nuclei (or zeolite crystals)zeolite A... 

The title Spectroscopy in Catalysis is attractively compact but not quite precise. The book also introduces microscopy, diffraction and temperature programmed reaction methods, as these are important tools in the characterization of catalysts. As to applications, I have limited myself to supported metals, oxides, sulfides and metal single crystals. Zeolites, as well as techniques such as nuclear magnetic resonance and electron spin resonance have been left out, mainly because the author has little personal experience with these subjects. Catalysis in the year 2000 would not be what it is without surface science. Hence, techniques that are applicable to study the surfaces of single crystals or metal foils used to model catalytic surfaces, have been included. 

Taking the crystallinity parameter QA (external standard [6]) as a measure for content of crystallized zeolite. Starting Si02/Al203-ratio in the reaction mixture was 69. The QAi-values of about 1 are representing a tranformation of 100% into the zeolitic material. 

Crystals, Zeolites, Solid Host-Guest Complexes... 

I (semiconductors, optical crystals, zeolites, solar panels, gemstones, LCDs)... 

Qtudies of new perspective fine porous crystal zeolites have shown that their properties depend strongly on cations compensating the negative charge of the aluminosilicate framework. 

In order to verify the diffusion through the crystals, we investigated the steady-state diffusion of a number of organic vapors in granules of zeolite CaA and NaX 12, 13). The experiments were carried out in the presence of carrier gas at atmospheric pressure. Granules of commercial zeolite samples were secured with hermetizing paste into the orifice of an aluminum membrane, and powdered crystallic zeolite was pressed into the orifice. 

Scandella L, Binder G, Mezzacasa T, Gobrecht J, Berber R, Lang HP, Gerber CH, Gimsewski JK, Koegler JH, and Hansen JC. Combination of single crystal zeolites and microfabrication Two applications towards zeolite nanodevices. Micropor Mesopor Mater 1998 21(4-6) 403 09. 

M. Morris, A. Dixon, A. Sacco, and R. Thompson, Investigation on the Relative Effectiveness of some Tertiary Alkanolamines in the Synthesis of Large-crystal Zeolite NaA. Zeolites, 1993, 13, 113-121. 

A. Persson, B. Schoeman, J. Sterte, and J. Otterstedt, Synthesis of Stable Suspensions of Discrete Colloidal Zeolite (Na, TPA) ZSM-5 Crystals. Zeolites, 1995, 15, 611-619. 

Powerful evidence for the liquid-phase mechanism comes from the direct crystallization of zeolite from clear solution. In the early 1980s, Koizumi and coworkers carried out an extensive study on this topic. They directly synthesized analcime, hydroxysodalite, zeolite B, mordenite, zeolite P, faujasite,[30] erionite, and potassium chabazite from clear solution. Pang et al. directly crystallized zeolite A[31] and FAPO-5[32] from clear solution as well. The study on the direct synthesis of faujasite [30, 33] from clear solution will be elaborated below. 

A schematic picture of different t5q)es of pores is given in Fig. 9.1 and of main types of pore shapes in Fig. 9.2. In single crystal zeolites the pore characteristics are an intrinsic property of the crystalline lattice [3] but in zeolite membranes other pore types also occur. As can be seen from Fig. 9.1, isolated pores and dead ends do not contribute to the permeation under steady conditions. With adsorbing gases, dead end pores can contribute however in transient measurements [1,2,3]. Dead ends do also contribute to the porosity as measured by adsorption techniques but do not contribute to the effective porosity in permeation. Pore shapes are channel-like or slit-shaped. Pore constrictions are important for flow resistance, especially when capillary condensation and surface diffusion phenomena occur in systems with a relatively large internal surface area. 

A theoretical model describing gas transport in microporous (single crystal zeolite) membranes in regions a and bi of Fig. 9.20 was proposed by Barrer [85] and is schematically given in Fig. 9.21. 

Zeolite Crystals and Sieves. Making Matter. Available from crystals/zeolites.html>. 

The purpose of this study has been to synthesize new crystalline phases of beryllosilicate with zeolitic structure. The first attempt was made to obtain a phase with the analcime-like structure, because it is known that analcime is the most easily crystallized zeolitic phase under hydrothermal conditions in the system Na20-Al203-Si02-H20. 

Zeolite NaA and FAU crystals were grown under the same hydrothermal condition using the same composition of clear solution. The only difference was the type of seed crystal used. This result suggested that the crystal growth did not occur by the attachment of nano-crystals. Zeolite films/membranes were prepared by the growth of seeded crystals. Based on the SEM and TEM observations and single gas permeation measurements, densification model of film/membrane is presented. 

A polymer must, by its very nature, be accommodated in the pores rather than in the small cages of a crystallizing zeolite structure. In the... 

Membrane Wicke Kallenbach Single crystal Zeolite membrane Catalyst effectiveness factor... 

---