For zeolite

Treacy M M J, Fliggins J B and von Ballmoos R 1996 Collection of Simulated XRD Powder Patterns for Zeolites 3rd revised edn (London Elsevier)... 

Structure-based Design of Templates for Zeolite Synthesis... 

M Falciom, MW Deem. A biased Monte Carlo scheme for zeolite structure solution. I Chem Phys 110 1754-1766, 1999. 

In this section, an attempt is made to sketch the current status of zeohte MRs with respect to specific applications. The application of zeohte MRs is strongly related to the development status of zeolite membranes. Topics that are discussed are the most often studied reactions for zeolite membrane apphcations dewatering. 

An important driver for zeolite membrane apphcations has been the commercialization of the NaA membranes for dehydration. However, for these membranes, the quality required is not as high as compared to gas-phase molecular sieving... 

Models of regular structures, such as zeolites, have been extensively considered in the catalysis literature. Recently, Garces [124] has developed a simple model where the complex pore structure is represented by a single void with a shell formed by n-connected sites forming a net. This model was found to work well for zeolites. Since polymer gels consist of networks of polymers, other approaches, discussed later, have been developed to consider the nature of the structure of the gel. 

Natural zeolites may bear the name of the mineral (mordenite, faujasite, ferrier-ite, silicalite), or sometimes that of the discoverer, e.g. Barrerite after Professor Barrer, or the place where they were found, e.g. Bikitaite from Bikita, Zimbabwe. Synthetic zeolites are usually named after the industry or university where they were developed, e.g. VPI comes from Virginia Polytechnic Institute, and ZSM stands for Zeolite Socony Mobil. 

These results being quite untypical for zeolites give rise to a number of fundamental questions i) what makes the zeolite to function as an active catalyst ii) what makes N2O to function as a selective oxidant iii) what is the reaction mechanism. We shall shortly discuss the situation with these issues because of their importance for our further consideration. 

Pentene oxidation over TS-1 catalyst is a fast reaction and hence fulfils a basic requirement for being suited to micro-channel processing [30]. Thus, it can serve as a model reaction to demonstrate the benefits of micro chemical engineering, particularly for zeolite-catalyzed reactions. Apart from this, epoxidations are an important class of organic reactions, also of industrial importance. 

Figure 3.24. Schematic representation of early synthesis method for zeolites (Van Bekkum et al, 1991).

Hydrothermal alteration minerals from midoceanic basalt are analcite, stilbite, heulandite, natrolite-mesolite-scolecite series, chlorite and smectite for zeolite facies, prehnite, chlorite, calcite and epidote for prehnite-pumpellyite facies, albite, actinolite, chlorite, epidote, quartz, sphene, hornblende, tremolite, talc, magnetite, and nontronite for green schist facies, hornblende, plagioclase, actinolite, leucoxene, quartz, chlorite, apatite, biotite, epidote, magnetite and sphene for amphibolite facies (Humphris and Thompson, 1978). 

Table 2 Porosymmetry and Particle Size Data for Zeolites ...

Figure 241. Thermal breakthrough curves (adsorption) for Zeolite and Silicagel...

Figure 241 shows the shape of two thermal breakthrough curves for Zeolite and Silicagel in adsorption. The adsorption is following a desorption using 130 °C and the inlet air is saturated with water vapor at 25 °C. 

Figure 3 2D 27Al-29Si RAPT-CP-CPMG HETCOR data for zeolite ZSM-4 recorded at 14.1 T with 10 kHz MAS. The 2D spectrum was acquired in 30 rows of hypercomplex data, with 64K scans per row, h increments of 100 ps, and acquisition time of 38 hours. In the right, ID slices taken through the centers of Ah and Al2 resonances are compared with ID 29Si MAS spectrum.

IR and Raman spectroscopy can fulfill these requirements and they are also robust enough for in situ silicate analysis in plant reactors [7]. Both of these techniques have been used for identifying the symmetric (s) and asymmetric (as), stretching (va, vas) and bending (5a, 5as) O-Si-O vibrations in aqueous alkaline silicate solutions which are the cheapest hence most frequently used ingredients for zeolite synthesis [8, 9 and references herein]. However, this information has to be "translated" into siloxane ring... 

DRIFT spectroscopy was used to determine Av0h shifts, induced by adsorption of N2 and hexane for zeolite H-ZSM-5 (ZSM-a and ZSM-b, Si/Al=15.5 and 26), H-mordenite (Mor-a and Mor-b, Si/AI— 6.8 and 10) and H-Y (Y-a and Y-b, Si/Al=2.5 and 10.4) samples. Catalysts were activated in 02 flow at 773 K in situ in the DRIFTS cell and contacted than with N2 at pressures up to 9 bar at 298 K or with 6.1% hexane/He mixture at 553 K, i.e., under reaction conditions. Catalytic activities of the solids were measured in a flow-through microreactor and kapp was obtained as slope of -ln(l-X0) vs. W/F plots. The concentration of Bronsted acid sites was determined by measuring the NH4+ ion-exchange capacity of the zeolite. The site specific apparent rate constant, TOFBapp, was obtained as the ratio of kapp and the concentration of Bronsted acid sites. 

As has been confirmed by XRD, the framework of montmorillonite has been partly destroyed due to the calcination under high temperature. Most diffraction peaks of montmorillonite are faint. After hydrothermal crystallization the characteristic Bragg reflections for zeolite Beta structure at 7.7° and 22.42° 20 are detected in the composite, indicating the presence of the Beta phase. 

The ease with which chitosan hydrocolloid gels can be casted and functionalised has prompted their use as matrices for zeolites in pervaporation membranes and as binders of adsorbents and catalysts [3,4]. 

---