Mordenite composition

The reactants used for mordenite synthesis were an amorphous substrate of near-mordenite composition (Zeolex S-6-10, 0.91 Na -AkOa-10.6 Si02-7.4 H20, J. M. Huber Co.) and two different types of sodium sili-... 

Crystallization was followed by analyzing the solid product quantitatively by x-ray powder diffraction. Prepared mixtures of a standard sample of mordenite and the amorphous substrate of mordenite composition were used to establish a calibration curve for the quantity of mordenite based on the summation of x-ray peak intensities. For zeolites A and X, the unreacted aluminosilicate gel was used to prepare mixtures with standard samples of zeolites A and X for quantitative phase identification. 

Mordenite can be synthesized from gels comprised of Na2<), AI2O3, Si02 and H2O (9-13). More siliceous products are formed as the Sit /A C and Si02/Na2<) ratios are increased (13). The range of mordenite compositions which can be prepared as pure phases by this method are represented in Formula 1. 

Yoonoo C, Dawson CP, Roberts EPL, Holmes SM (2011) Nafion/mordenite composite membranes for improved direct methanol fuel cell performance. J Membr Sci 369 367-374... 

Polyvinyl alcohol/mordenite composite membrane prepared using appropriate quantity of mordenite and heat treatment could significantly reduce the permeation of methanol molecules [27]. However, to achieve this improvement, there should be a suitable tailoring of the transport properties between the polymer and zeolite... 

With over 600 currently known zeolites and new ones discovered every year, it is useful to have a general classification of structures endorsed by the lUPAC. In this system each structure has three letters, for example EAU for faujasites, MFI for ZSM-5 and MOR for mordenite. Within a given structure there can still be many different zeolites, as the composition may vary. 

Conclusive evidence has been presented that surface-catalyzed coupling of alcohols to ethers proceeds predominantly the S 2 pathway, in which product composition, oxygen retention, and chiral inversion is controlled 1 "competitive double parkir of reactant alcohols or by transition state shape selectivity. These two features afforded by the use of solid add catalysts result in selectivities that are superior to solution reactions. High resolution XPS data demonstrate that Brpnsted add centers activate the alcohols for ether synthesis over sulfonic add resins, and the reaction conditions in zeolites indicate that Brpnsted adds are active centers therein, too. Two different shape-selectivity effects on the alcohol coupling pathway were observed herein transition-state constraint in HZSM-5 and reactant approach constraint in H-mordenite. None of these effects is a molecular sieving of the reactant molecules in the main zeolite channels, as both methanol and isobutanol have dimensions smaller than the main channel diameters in ZSM-S and mordenite. 

Figure 44.3. Conversion of methanol (O), yields of alkylaromaties (A) and yields to light componnds (CO + CO2 + CH4) (O) as functions of temperature. Feed composition (molar fractions) methanol 0.12, nitrogen 0.88. Catalyst H-mordenite.

Figure 44.5. Conversion of phenol ( ), molar selectivity to anisole (X), o-cresol (O), p-cresol (A), 2,6-xylenol (O), salicylaldehyde ( ) and polyalkylated phenols ( ) as functions of temperature. Catalyst H-mordenite. Feed composition N2 89.3%, formaldehyde 1.7%, phenol 0.46%, methanol 0.03% and water 8.5%.

The zeolites-chitosan composites were prepared by adding a known amount of zeolite (X, Y, or mordenite) into a 3 % chitosan solution in 1 % aqueous acetic acid. The zeolite powder was dispersed in the chitosan solution and stirred at room temperature during 1-2 hours. The gelling procedures were later carried out like as in the absence of zeolites. 

Figure 2. Scanning electron microscopy of (a) zeolite X-chitosan, (b) zeolite Y-chitosan and (c) mordenite-chitosan composites prepared by encapsulation of zeolites during the gelling of chitosan.

Because BaO/NaX zeolite catalysts exhibited the best performance, further investigations have been carried out recently to characterize the oxidative methylation of toluene catalyzed by BaO-modified X- and Y-zeolites, mordenite, ZSM-5, sil-icalite, and ALPO4-5 (230). The authors found that activity and basicity of BaO-modified zeolites and zeolite-like catalysts depend on both the structural type and composition. Thus, for samples of the same structural type (BaO/NaX zeolite. 

Fig. 2. Composition diagram for the reactant and suitable temperature for synthesis of high silica mordenite.

The major aluminous clay minerals, alkali zeolites and feldspars which are most commonly associated in nature can be considered as the phases present in a simplified chemical system. Zeolites can be chemiographically aligned between natrolite (Na) and phillipsite (K) at the silica-poor, and mordenite-clinoptilolite at the silica-rich end of the compositional series. Potassium mica (illite), montmorillonite, kaolinite, gibbsite and opal or amorphous silica are the other phases which can be expected in... 

He = heulandite Cl = clinoptilolite Mor = mordenite M = mica. Solid solution or continuous compositions are assumed present between analcite and mordenite-clinoptilolite. 

Figure 1. Crystallization curves of mordenite from a batch composition 8.5 N avO-AWz-85 SiD2 182 H20 as a function of temperature and NaCl content filled symbols, no NaCl open symbols, 4.5 moles of NaCl/mole Al2Oz)...

The fast conversion rate of amorphous batch into mordenite, once the crystallization has started, indicates that the rate-limiting step in the overall process is the nucleation. To substantiate this, mordenite was crystallized with the same batch composition but with the addition of seed... 

Figure 8. The effect of seeding on crystallization rates of mordenite from a hatch composition of 8.6 NazO-AWr-85 SiOz-182 HzO 4-5 NaCl as a function of temperature (8X2X8 imeter seed crystals)...

This study showed that the overall crystallization processes for mor-denite, zeolite X, and zeolite A were similar. However, the physical properties of the crystallizing system determine the rate-limiting step for a particular zeolite synthesis. In the case of mordenite in which both the viscosity of the batch composition and the morphology of seed crystals were varied, it was observed that diffusion in the liquid phase was the ratedetermining step. For zeolite X the actual growth rate on the crystal-liquid interface was the rate-limiting factor as shown by identical conversion rates for the seeded and unseeded systems. For zeolite A in the system chosen, both processes influenced the conversion rate. 

---