Mordenite synthesis

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-... 

Syntheses were run in modified Morey-type autoclaves of 15-ml capacity at autogenous pressure. For mordenite synthesis, the reactants were mixed in a mortar and pestle into a homogeneous mix and loaded into the autoclaves. For zeolite A and X synthesis, separate sodium aluminate solutions and colloidal silica sols were prepared and mixed in the autoclaves. 

Mordenite and ZSM-5 are synthesized at lower pH values, and it is not surprising that in these conditions silicate species are not usually observed in solution [27,29]. In both cases, the solid initially resembles vitreous silica. In the case of ZSM-5, new vibrations in the solid phase are only observed when ZSM-5 crystals appear [27]. More information concerning the intermediate synthesis steps can be retrieved from mordenite synthesis spectra [29]. In mordenite synthesis, a 495 cm band is observed at an early stage in the spectrum of the solid fraction of the gel. In analogy to what is observed for A and X zeolites, this band is ascribed to 4MR aluminosilicate units. Only at a later stage, broader bands appear at 402 and 465 cm, indicative of the formation of still rather... 

Within the crystallisation field of a given zeolite, increasing the alkalinity has a similar effect upon the kinetics of crystallisation as a rise in temperature. This is illustrated in Fig. 8 [69] for mordenite synthesis from gels at a series of increasing pH values. This figure is to be compared with Fig. 1 for the same zeolite at a series of increasing temperatures. Fig. 8 also shows that at pH 13.3 the mordenite first formed dissolves. Its succesor is analcime. 

Figure 8. Influence of pH upon curves of yield against time for mordenite synthesis at 300 C [69],...

Selective synthesis of ethylenediamine from ethanolamine over modified H-mordenite catalyst... 

The synthesis of ethylenediamine (EDA) from ethanolamine (EA) with ammonia over acidic t3pes of zeolite catalyst was investigated. Among the zeolites tested in this study, the protonic form of mordenite catalyst that was treated with EDTA (H-EDTA-MOR) showed the highest activity and selectivity for the formation of EA at 603 K, W/F=200 g h mol, and NH3/ =50. The reaction proved to be highly selective for EA over H-EDTA-MOR, with small amounts of ethyleneimine (El) and piperazine (PA) derivatives as the side products. IR spectroscopic data provide evidence that the protonated El is the chemical intermediate for the reaction. The reaction for Uie formation of EDA from EA and ammonia required stronger acidic sites in the mordenite channels for hi er yield and selectivity. 

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. 

The formation of such bonds during the heat treatment of dealuminated mordenite has also been suggested by Rubinshtein et al. (72-74), in some instances without the intermediate formation of SiOH groups. The hydrophobic nature of the zeolite also increases with progressive dealumination. Chen (71) has shown that aluminum-deficient mordenite zeolites with SiO /Al O ratios over 80 absorb little or no water at low pressure. These highly silicious zeolites are truly hydrophobic and in this respect are similar to highly silicious zeolites prepared by direct synthesis (e.g. ZSM-5) (75). 

Sand, L.B. (1968) Synthesis of large-port and small-port mordenites. Mol. Sieves, Pap. Conf, 1967, 71-77. 

Experimental and computational study of beta, ZSM-12, Y, mordenite and ERB-1 in cumene synthesis. Micropor. Mater., 6, 395-404. 

Boveri, M., Marquez-Alvarez, C., Laborde, M.A., and Sastre, E. (2006) Steam and add dealumination of mordenite charaderization and influence on the catalytic performance in linear alkylbenzene synthesis. Catal. Today, 114, 217-225. 

As mentioned above, the main types of zeoHtes in industrial catalytic application today are Zeolite Y (FAU) and its variants, ZSM-5 and SUicahte (MFI), Mordenite (MOR) and Beta (BEA). After the first commercial synthesis of X and Y zeolites in the mid- to late 1940s by workers at the Union Carbide Corporation [21, 22],... 

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

With zeolites as the solid acid catalyst, the best results for HMF synthesis were obtained by Moreau et al. who tested acidic mordenites with different Si/Al ratios in batch experiments and reported that dealuminated H-Mordenite with Si/Al ratio of 11 exhibited the highest selectivity and even so at reasonably high fructose conversion (91% selectivity at 76% conversion after 60 min. at 165 °C using water/methyl isobutyl ketone as the reaction media).Other zeolites, H-Y, H-Beta and H-ZSM-5 were also tested for the reaction, however, none of these catalysts were as selective as H-mordenite. ... 

Sr mordenite synthesized by Barrer and Marshall (16) gave the Cmcm x-ray pattern and was C-centered orthorhombic by electron diffraction. However, other electron diffraction studies, also by Kerr (12), revealed some synthetic Sr mordenite crystals of the Immm structure prepared at similar synthesis conditions. Future work should examine synthetic Sr and Ca mordenite specimens further for the possible presence of other framework structures, and correlation of structures with Sr2+/Ca2+ ion exchange selectivity. 

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. 

The synthesis of Ti-mordenite has been conducted by reaction of TiCl4 with dealuminated mordenite or by hydrothermal synthesis (Section IV.F). The evidence for the incorporation of titanium is limited. The UV-visible spectra show that, in addition to the transition at 48,000 cm- , assigned to isolated Tiiv in tetrahedral coordination, there is also an absorption at 35,000 cm-, indicating extra-framework Ti02. The catalytic properties in oxidation reactions with H202 are significantly different from those of Ti02 deposited on mordenite, but they are limited to the hydroxylation of benzene and the oxidation of w-hexane (Kim and Cho, 1993). 

Ti-Mordenite has been obtained by reaction of TiCI4 with dealuminated mordenite and by hydrothermal synthesis. The reaction of TiCl4 with dealuminated mordenite was carried out at 723 K following the method of Kraushaar and van Hooff (1988, 1989). In the hydrothermal synthesis, Si02 powder, NaOH, Al isopropoxide, and TBOT react at 448 K for 3 days (Kim et al., 1993). 

Zeolite-supported Re catalysts have been synthesized by chemical vapor deposition (CVD) ofMTO (CH3Re03) (3) on various zeolites such as HZSM-5, H-Beta, H-USY and H-Mordenite. HZSM-5 samples with different A1 contents were prepared by a hydrothermal synthesis method. For comparison, conventional impregnated catalysts were also prepared by an impregnation method using an aqueous solution of NH4Re04. All catalysts were pretreated at 673 K in a flow of He before use as catalyst. 

Machado et al. (1) studied the synthesis of monolaurin from lauric acid and glycerol employing commercial Beta, Y, and Mordenite zeolites as catalysts. The optimized conditions for the monolaurin synthesis... 

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