Pure zeolites

Another example of performance enhancement using a zeolite/TUD-1 catalyst is shown in n-hexane cracking using a series of zeolite-Beta-embedded TUD-1 catalysts (29) 20, 40 and 60 wt% zeolite Beta in Al-Si-TUD-1 (Si/Al = 150). These are compared to pure zeolite Beta, and to a physical mixture of 40% zeolite Beta and 60% Al-Si-TUD-1. These catalysts were tested in a fixed bed reactor, at atmospheric pressure, with constant residence time at 538°C. The pseudo-first-order rate constants are shown in Figure 41.8. Note that the zeohte-loaded catalysts were clearly superior to both the pure zeolite Beta catalyst and the zeohte-TUD-1 physical mixture. Again, this is evidence that catalyst performance benefits from a hierarchical pore stracture such as zeolite embedded in TUD-1. 

The highly oxygenated bio oil can be de-oxygenated, and thereby upgraded, over acidic zeolite catalysts through the formation of mainly water at low temperatures and C02 and CO at higher temperatures [1-3], Successful catalytic pyrolysis of woody biomass over Beta zeolites has been performed in a fluidized bed reactor in [4]. A drawback in the use of pure zeolitic materials has been the mechanical strength of the pelletized zeolite particles in the fluidized bed. 

Pyrolysis and catalytic de-oxygenation of pine wood biomass was successfully carried out in a dual-fluidized bed reactor. Hybrid catalysts consisting of zeolites Beta and ZSM-5 and bentonite were used. Pure zeolites Beta and ZSM-5 and also pure bentonite were tested as bed materials in the fluidized bed reactor. 

Attrition problems previously noticed by the present authors in the use of pure zeolitic materials were not observed in any of the experiments reported here, indicating that the addition of bentonite as a binder to the zeolites improved the mechanical strength. 

In this chapter, we describe the design and important properties of supra-molecularly organized dye molecules in the channels of hexagonal nanocrystals. We focus on zeolite L as a host. The principles, however, hold for other materials as well. As an example, we mention ZSM-12 for which some preliminary results have been reported [55], We have developed different methods for preparing well-defined dye-zeolite materials, working for cationic dyes, neutral dyes, and combinations of them [3, 22, 25, 52], The formula and trivial names of some dyes that so far have been inserted in zeolite L are reported in Section II.C. The properties of natural and commercially available zeolites can be influenced dramatically by impurities formed by transition metals, chloride, aluminiumoxide, and others. This fact is not always sufficiently taken care of. In this chapter, we only report results on chemically pure zeolites, the synthesis of which is described in [53]. 

The Maxwell model can also guide the selection of a proper polymer material for a selected zeolite at a given volume fraction for a target separation. For most cases, however, the Maxwell model cannot be applied to guide the selection of polymer or zeolite materials for making new mixed-matrix membranes due to the lack of permeabihty and selectivity information for most of the pure zeolite materials. In addition, although this Maxwell model is well-understood and accepted as a simple and effective tool for estimating mixed-matrix membrane properties, sometimes it needs to be modified to estimate the properties of some non-ideal mixed-matrix membranes. 

Removal of about half of the linear polymer by solvent extraction left individual zeolite crystals containing the remaining polymer. Scanning electron micrographs showed there was essentially no polymer between or on the zeolite (observable before the extraction), and resembled micrographs of the pure zeolite. All linear polymer could be removed on extended solvent extraction. 

Early work was done with a sized fraction (about 0.1 mm) obtained by grinding zeolite pellets which contained a significant amount of binder. Subsequently, the pure zeolite powder was used. In all cases the zeolite was washed with a large volume of dilute salt solution, sometimes containing a small amount of acetate buffer at about pH 5.5, and precautions were taken to avoid hydrolytic precipitation of the metals. 

Figure 3a is a schematic of the functionalized zeolite beta. Figure 3b plotted the catalytic conversion of HEX and PYC over 6 A zeolites as a function of time. For sulfonated zeolite (Z-S03H), more than 60 % HEX was converted in 4 hours, and nearly complete conversion was observed over 12 hours. On the other hand, PYC, which has a large molecular size and cannot enter the microporosity, showed less than 8 % conversion over extended reaction time with same Z-S03H as catalyst. Both HEX and PYC were also reacted over pure zeolite beta (Z), and the TMMPS functionalized zeolite (Z-SH) before it was treated with H202. Pure zeolite and Z-SH showed low catalytic activity, and only a small fraction of either HEX or PYC was converted. Further evidence of the size selectivity is provided when amines of different sizes are used to poison (neutralize) the acid sites (19). As shown in Figure 3c, the... 

SEM/EDX analyses were done with a Philips PV9800 EDX spectrometer. An acceleration potential of 25 or 30 kV was used for the EDX measurement (2 micron depth analysis). Care was taken to find both pure matrix and pure zeolite spots. Multi-spot analyses were performed on different particles of a sample in order to obtain more accurate information. Quantitative calculations were done with the Super Quant program with a ZAF correction to obtain relative concentrations. 

I first identified the X zeolite by its x-ray peaks as an impurity in the B zeolite in 1949 at about a 20% concentration. We next saw it in February 1950 at about a 50% concentration with the B zeolite when N. R. Mumbach brought in the x-ray pattern from his first attempt to scale up the synthesis of B. By mid 1950, I had discovered how to routinely make pure zeolite X [11]. Chabazite was synthesized in late 1950, and by mid 1951 I had made three new... 

We describe a systematic investigation of various synthesis variables that usually affect the crystallization of faujasite-type structures from Si, Al, Na, tetraethylammonium (TEA) hydrogels.A careful control of parameters such as the composition of the precursor hydrogel, temperature and crystallization time is needed to selectively prepare and stabilize pure zeolite ZSM-20 in high yield. 

Given a set of synthesis conditions and sufficient reaction time to produce hydroxysodalite, pure zeolite A can be obtained by decreasing the reaction time until the % HS approaches 0. If the reaction time is fixed, any of the other variables can be varied and achieve the same result. An example of how reaction time affects the conversion of zeolite A to hydroxysodalite, when all other variables are held constant, appears on Figure 9. 

The samples used in this study were both natural and synthetic varieties of mordenite and are listed in Table I. Each material contained more than 95% pure zeolite with the remainder being amorphous material as measured by x-ray diffractometry. Before being used in experimentation, each sample was exchanged to the sodium form. 

The structural features of dealuminated zeolite samples were characterized using X-ray powder diffraction, porosimetry and solid-state NMR measurements. Hexadecane cracking was used as a probe reaction to investigate catalytic properties of pure zeolites. 

Blatter, F. Schumacher, E. The Preparation of Pure Zeolite NaY and its Conversion to High-Silica Faujasite, J. Chem. Educ. 1990, 67, 519-521. 

Fig.l and Fig.2 show the XRD and SEM images of the products which were obtained from the mixtures with Si02/Al203 = 100 on the base of Al(OH)3 and NaF without any pretreatment (a), with stirring by magnetic bar (b) and ball-milling (c) before crystallization. As seen from these figures the pure zeolite MWW crystallized only from the mixture milled on Planet Mill. Otherwise kenyaite and MTW were the main phases. 

No pure zeolite MWW was obtained from the mixtures on the base of NaOH (Fig.3). MWW with kenyaite impurity was formed after crystallization of mixtures with Si02/Al203 = 100 for 7-10 days. Pure kenyaite was the main phase in the case of crystallization of the mixtures with Si02/Al203 = 200. The increase of the synthesis time up to 14 days leads to formation a-quartz [10]. Only slightly difference was observed between the samples crystallized with or without ball milling and without pretreatment. 

Batch experiments were performed at 298 K via a standard volumetric method, using a 1.1 L glass reactor at atmospheric pressure, containing typically 0.5 g of adsorbent, polluted by liquid VOC injection, leading to an initial concentration of about 0.5 mmol.L. Equilibrium times were 1 and 2 hours respectively for Fau Y and Sil Z, after which the gas phase was sampled and analysed by chromatography (HP 5890II). Using the conventional assumption that the clay binder does not take part in the adsorption mechanism, data were reported for pure zeolite material. Reproducibility and repeatability of experimental data were checked by three different manipulators. 

Figu re 8.14 Estimate of the platinum content in each of the constituents of a zeolite-alumina mixture (jr 0 pure zeolite, x = 1 pure alumina). 

Magnesia has strong basic sites but no acid sites (Table XVII) (e.g., 147, 179,180,189,203). However, acidity is generated when magnesia is added to silica (Table XVIII) (74,104). This acidity is exclusively of the Lewis type (59). Its acid sites are more widely distributed as compared with silica-alumina. The acid strength distribution of amorphous silica-alumina and silica-magnesia is more heterogeneous than that observed for any of the pure zeolites (H Y, ZSM-5, mordenite, etc.). This may in part be due to the presence of surface Al and Mg cations located in different environments. 

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