Beta dealumination

The FTIR/KBr method was, inter aha, applied by Maache et al. [306] for the characterization of various samples of H-Beta dealuminated by acid leaching. In the case of framework vibrations of zeolite Beta, a good Hnear correlation was found between the wavenumber of the asymmetric O-T-O vibration, Vas(O T-o)> and the aluminum mole fraction, nAi/(nsj+nAi) [263]. Ponthieu et al. [307] attempted to find a correlation between the wavenumbers of framework vibrations of ojfretite and zeolite Omega and the degree of dealumination (aluminum mole fraction) similar to those observed with faujasites and mordenites. However, Hnear correlations were hardly obtained. 

Maache, M., Janin, A., Lavalley, J.C., Joly, J.F., Benazzi E. (1993). Acidity of Zeolites Beta Dealuminated by Acid Leaching An FTi.r. Study Using Different Probe Molecules (Pyridine, Carbon Monoxide). Zeolites, Vol.l3, No.6, (July-August 1993), pp. 419-426, ISSN 0144-2449... 

MicrocrystalUne zeolites such as beta zeolite suffer from calcination. The crystallinity is decreased and the framework can be notably dealuminated by the steam generated [175]. Potential Br0nsted catalytic sites are lost and heteroatoms migrate to extra-framework positions, leading to a decrease in catalytic performance. Nanocrystals and ultrafine zeolite particles display aggregation issues, difficulties in regeneration, and low thermal and hydrothermal stabilities. Therefore, calcination is sometimes not the optimal protocol to activate such systems. Application of zeolites for coatings, patterned thin-films, and membranes usually is associated with defects and cracks upon template removal. 

In view of catalytic potential applications, there is a need for a convenient means of characterization of the porosity of new catalyst materials in order to quickly target the potential industrial catalytic applications of the studied catalysts. The use of model test reactions is a characterization tool of first choice, since this method has been very successful with zeolites where it precisely reflects shape-selectivity effects imposed by the porous structure of tested materials. Adsorption of probe molecules is another attractive approach. Both types of approaches will be presented in this work. The methodology developed in this work on zeolites Beta, USY and silica-alumina may be appropriate for determination of accessible mesoporosity in other types of dealuminated zeolites as well as in hierarchical materials presenting combinations of various types of pores. 

In all cases, the high activity and selectivity of this zeolite as compared to other three-dimensional zeolites, such as beta or dealuminated Faujasite zeolite, is related to the easier and/or faster diffusion of the products and to minimization of undesired consecutive reactions. 

Seeding technique. Al-free Ti-beta obtained by use of dealuminated zeolite-beta seeds Fluoride method. Al-free Ti-beta synthesis from a reaction mixture containing TEAOH and fluoride ions (HF) at near-neutral pH. Gel composition Ti02 60SiO2 32.9NEt4OH 32.9HF 20H2O 457.5 H20. Crystallization at 413 K with rotation of the autoclave (60 rpm)... 

Isomaltose from isomaltose, glucose Dealuminated-beta zeolite Water/ethanol [228]... 

Separation of isomaltose from high sugar concentrated enzyme reaction mixture by dealuminated beta-zeolite. Sep. Purif. TechnoL, 38,129. 

A very shallow maximum in activity for both n-heptane and gasoil cracking is observed for Beta zeolites (with nominal framework Si/Al ratio of 20-40), while for Y zeolite a clear maximum is located at values between 10 and 20. In any case, a partial dealumination takes place when the TEA-3 zeolites are NHj-exchanged and calcined. Consequently, the activity curve for Beta zeolites should be shifted to higher framework Si/Al with respect to those plotted in Figures 6 and 7a. 

Beta zeolite is partially dealuminated by deep bed calcination, and octahedral aluminum is then detected by 27 1 MAS NMR. Dealumi-nation is higher when lower the initial framework Si/Al ratio. 

In order to avoid the acid-catalyzed dehydration of sorbitol to isosorbide, Corma et al. reported a new innovative three-step cascade route involving (1) an acetaUza-tion of sorbitol, (2) an esterification of sorbitol, and (3) a deacetalization of sorbitol esters (Scheme 14) [131]. In this case, esters of sorbitol were obtained. At 408 K, between 70 and 90% of conversion of sorbitol was obtained. Activity of the zeolites employed (H-Beta, mordenite, and dealuminated zeolite ITQ-2) was dependent on both their acidity and pore structure. The modemite catalyst has emerged as the most efficient. 

Inevitably, the zeolites with a Spaciousness Index between 2 and 16 have a higher Si/Al ratio than zeolites Y or ZSM-20. To separate the effects of the Si/Al ratio and the pore width, two dealuminated samples of zeolite Y, designated YDl and YD2, were tested which resembled in their Si/Al ratios the Beta and EU-1 sample, respectively. Table 1 gives the isomerization selectivities at 40 % conversion. While dealumination of zeolite Y brings about some improvement in selectivity, H-Beta is clearly superior to HYDl, and H-EU-1 is a much better catalyst than HYD2, which indicates that the pore width in the appropriate range is of prime importance. 

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. ... 

Highly regioselective dialkylation of naphthalene was performed with 2-propanol380 and tert-butyl alcohol381 over dealuminated H-mordenite, and with tert-butyl alcohol over HY and Beta zeolites.382 Selectivities are within 60-84%. Computational modeling showed that the kinetic diameter of the 2,6-disubstituted isomer is smaller than that of the 2,7 isomer, which may explain the selective formation of the former within the appropriate zeolitic framework.382... 

Mordenite samples (MOR) were obtained from different sources (ref.5). Zeolites beta (BETA), mazzites (MAZ), offretites (OFF) and ZSM5 were synthesized according to procedures described elsewhere (refs.10-12). Some parent offretites, mordenites and mazzites suffered hydrothermal treatments and acid leachings to obtain dealuminated materials (refs.13,14). A wide variety of samples were thus prepared with Si/Al ratios in the range BETA 6.3 < Si/Al < 31.5, ZSM5 13.2 < Si/Al < 44, OFF 3.4 < Si/Al < 26, MAZ 2.5 ( Si/Al < 5, MOR 4.4 < Si/Al < 39.5. The protonic forms of the zeolites, e.g. HZSM5, were obtained by calcination of the ammonium forms at different temperatures. 

The incorporation of TiIV in the crystal lattice of silicalite has been attempted by the reaction of TiCl4 with dealuminated ZSM-5 (Kraushaar et al., 1988) or deborated borosilicalite (Carati et al., 1990). The same reaction has been used in the attempt to incorporate titanium in the crystal lattice of zeolite beta, morde-nite or zeolite Y. In many cases catalytic properties have resulted, but the way in which the incorporation takes place has been questioned. Because of its molecular dimensions, TiCl4 cannot enter or leave the pore system of ZSM-5. It has been shown that 89% of the OH groups present in the preformed zeolite as SiOH remain unreacted after treatment at 573 K with TiCl4. The incorporation of titanium must therefore be limited to the outer part of the crystals or proceed through a severe chemical attack with removal of silicon and formation of a secondary pore system (De Ruiter et al., 1993). Deposits of Ti02 on the outer part of the crystal treated with TiCl4 have indeed been observed (Carati et al., 1990), as has abnormal behavior in the oxidation of phenol (Section V.C.3.c). 

Cerqueira and co-workers203 confirmed the appearance of the of the tetrahedral aluminium and phosphorus in AlPO-like crystalline structures both in beta (BEA) and in MOR zeolites treated with phosphoric acid. 31P MAS,27Al MAS and TQM AS NMR spectra permitted the species present in the samples to be assigned. Possibly, besides the the Altet-f species, other Al species are also taking part in the activity and selectivity of the catalysts. The formation of Alocl o P can also contribute to the increase in the activity by preventing further dealumination. Dual zeolite additives have no impact on the quality of naphtha when compared to MFI-based additives, which are used in the fluid catalytic cracking processes. 

Titanium Silicalite-2 (TS-2), structurally similar to TS-1, could be prepared likewise using tetrabutylammonium hydroxide as the template [13, 14]. Titanium aluminum Beta (Ti,Al-[3) was prepared by hydrothermal synthesis from amorphous silica, sodium aluminate, tetraethyltitanate and tetraethylammonium hydroxide [15]. The presence of A1 was necessary for the crystallization of the product. Al-free Titanium Beta (Ti-[3) could be obtained in the presence of particular templates, such as dibenzyldimethylammonium hydroxide [16]. Titanium Mordenite (Ti-MOR), conversely, was obtained by post-synthesis insertion of Ti to dealuminated Mordenite [17]. Ti-MWW (Ti-MCM-22) was obtained by the synthesis of the lamellar precursor of Ti,B-MCM-22 followed by acid treatment to remove most of the boron and extra-framework Ti and finally calcination to burn out the template and bring about the condensation of lamellae into the three-dimensional MWW structure [18]. Ti is present in a number of different environ-... 

Running the Fisher indole synthesis on an unsymmetrical phenyl hydrazone gives a mixture of 2,3-disubstituted indoles. For example, reaction of the phenyl hydrazone, 34, with acid can give both 35 and 36 (Eqn. 22.26). Soluble acids and Amberlyst-15 give these two products in a 75 25 ratio at 100% conversion. With an H-M catalyst they are formed in a 65 35 ratio but over a dealuminated H-beta zeolite, the selectivity is reversed and 36 is produced in an 82% yield at 100% conversion.62 n was proposed that the preferential formation of 36 over the H-beta catalyst was the result of a restricted transition state selectivity. ... 

Non-contact atomic force microscope (AFM) and N2 absorption measurements on beta zeolites reveal the extreme irregularity of the external crystal surface which can make up a considerable proportion of the total surface area. A catalytic test, the acylation of 2-methoxynaphthalene, shows that active sites on the outer surface play an important role in the catalytic activity of the zeolite. Attempts to influence the external surface area and its catalytic activity through synthesis or post-synthesis modification such as dealumination show that the principle influence on the external surface comes from the synthesis procedure. 

The framework aluminium in zeolite beta is very sensitive to calcination and ion-exchange and dealumination occurs even under very mild conditions [5-7]. 27a1 NMR shows that octahedrally coordinated aluminium is often present in calcined H-betas, although it has been suggested that at least some of this aluminium is still attached to the framework and can be reincorporated under the right conditions [6,7]. 

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