BEA zeolite

In the present study the effect of zeolite particle size (micro- vs. nano-particles) and N20 concentrations on ODHP is studied over Fe modified BEA zeolites. The feasibility of periodic reactivation over Fe-BEA catalysts by oxygen pulses for continuous C3H6 production has been also evaluated. 

Fe-zeolites were prepared using the NH4 form of BEA Si/Al = 13.5. Parent BEA zeolite (average particle size of 300 nm or 1pm) was dried at 150 °C for 4 h and then mixed with a solution of FeCl3 in acetyl acetone. After 12 h of mixing, excess of the solution was removed, the solid was dried at room temperature and heated under vacuum at 350 °C for 4 h. A sample was washed with distilled water and dried in an air at room temperature. Then, the remaining organic species in the Fe-zeolites was removed by calcination at 450 °C in air for 10 h. The produced catalysts contain 0.6 wt% of Fe. This preparation procedure predominantly provides iron introduction into cationic sites [3], Two types of catalysts were prepared, Fe-BEA with a particle size of 1 pm (Fe/m-BEA) and Fe-BEA with particle size of 300 nm (Fe/n-BEA). 

Figures 1 shows the catalytic performance of the Fe-BEA catalysts in the temperature range of 250-550 °C. It is clear from the figure that propylene yield depends on particle size of the parent BEA zeolite. Effect of the N20 concentration has been analyzed under reaction regimes RS-1 and RS-2. Increase in N20 concentration resulted in the same propene yields but increased the N20 conversion and decreased the selectivity toward propylene. At higher temperature has been obtained increases in the formation of the molecular oxygen which further accelerates production of the undesired carbon oxides. Thus, at lower feed concentration of N20, i.e. at 1 1 feed ratio of reactants (RS-1), formation of carbon oxides is suppressed and the selectivity of ODHP reaction is...

The nomenclature of zeolites is rather arbitrary and follows no obvious rules because every producer of synthetic zeolites uses his/her own acronyms for the materials. However, as mentioned before, at least the structure types of the different zeolites have a unique code. For example, FAU represents Faujasite-type zeolites, LTA Linde Type A zeolites, MFI Mobile Five, and BEA Zeolite Beta. The structure commission of the International Zeolite Association (IZA) is the committee granting the respective three-letter codes [4], Some typical zeolites, which are of importance as catalysts in petrochemistry, will be described in the following sections. 

Figure 4.30 Overlay of IR spectra during CO adsorption at 90 K on H-BEA zeolite. The diagonal arrows indicate whether the band is increasing or decreasing with increasing CO coverage.

Penkova, A., Dzwigaj, S., Kefirov, R., Hadjiivanov, K., and Che, M. (2007) Effed of preparation method on the state of BEA zeolites. A study by Fourier transform Ir spectroscopy of adsorbed CO and NO, temperature programmed reductions, and x-ray... 

Busco, C., Barbaglia, A., Broyer, M., Bolis, V., Foddanu, G.M., and Ugliengo, P. (2004) Charaderization of Lewis and Bronsted addic sites in H-MFI and H-BEA zeolites a thermodynamic and ab initio smdy. Thermochim Acta, 418, 3-9. 

The Fries rearrangement of PA over H-BEA zeolites, which is a simple reaction, was chosen to introduce the competition for adsorption on the zeolite catalysts and its role on the reaction rate. Ortho- and para-hydroxyacetophenones (o- and p-HAP), para-acetoxyacetophenone (p-AXAP) and phenol (P) are the main products o-HAP, P and p-AXAP, which are directly formed (primary products),... 

Figure 2.5 Relative occupancy (%) of the intracrystalline volume of a H-BEA zeolite during the transformation of a 2 1 molar anisole - acetic anhydride mixture in a batch reactor, assuming no adsorption of acetic acid and full occupancy of the micropores. Anisole ( ), acetic anhydride (o) and 4-methoxyacetophenone (x). Reprinted from Journal of Catalysis, Vol. 187, Derouane et al., Zeolite catalysts as solid solvents in Fine Chemicals synthesis 1. Catalyst deactivation in the Friedel-Crafts acetylation of anisole, pp. 209-218, copyright (1999), with permission from Elsevier...

Adsorption experiments The method developed for the analysis of carbonaceous compounds formed and trapped within the zeolite micropores during catalytic reactions1581 can be adapted for determining the occupancy of micropores by reactant, solvent and product molecules. However, this method cannot be used with compounds sensitive to hydrolysis, such as AA, because of the step of dissolution of the zeolite in a hydrofluoric acid solution necessary for the complete recovery of the organic molecules located within the zeolite micropores.[58] This method was used to determine the composition of the organic compounds retained within the micropores of three different zeolites [H-BEA (zeolite Beta), H-FAU (zeolite Y), and H-MFI (zeolite ZSM-5)] after contact in a stirred batch reactor at 393 K for 4 min of a solution containing 20 mmol of 2-methoxynaphthalene (2-MN), 4 mmol of l-acetyl-2-methoxynaphthalene (1-AMN) and 1 ml of solvent (sulfolane or nitrobenzene) with 500 mg of activated zeolite.[59 61] From the comparison of... 

Figure 3.1 Acetylation at 373 K with acetic anhydride of a series of aromatic compounds over HBEA-15 zeolite. Conversion (XSUB) of anisole ( ), 2-methoxynaphthalene (x), m-xylene ( ), toluene ( ), 2-methylnaphthalene (o) and fluorobenzene (a) versus time. Reprinted from Journal of Catalysis, Vol. 230, Guidotti et al. Acetylation of aromatic compounds with H-BEA zeolite the influence of the substituents on the reactivity and on the catalyst stability, pp. 375-383, Copyright (2005), with permission from Elsevier...

Whereas the acetylation of phenyl ethers over zeolite catalysts leads to the desired products, acetylation of 2-MN occurs generally at the very activated C-l position with formation of l-acetyl-2-methoxynaphthalene (l-AMN). A selectivity for l-AMN close to 100% can be obtained over silicoaluminate MCM-41 mesoporous molecular sieves[22] and FAU zeolites,133 341 whereas with other large pore zeolites with smaller pore size (BEA, MTW, ITQ-7), 2-AMN (and a small amount of l-acetyl-7-methoxynaphthalene, 3-AMN) also appears as a primary product. Average pore size zeolites, such as MFI, are much less active than large pore zeolites. These differences were related to shape selectivity effects and a great deal of research work was carried out over BEA zeolites in order to specify the origin of this shape selectivity the difference is either in the location for the formation of the bulkier (l-AMN) and linear (2-AMN) isomers (only on the outer surface for l-AMN, preferentially within the micropores for 2-AMN)[19 21 24 28 381 or more simply in the rates of desorption from the zeolite micropores.126 32 33 351... 

In addition to 2-MN acetylation, secondary reactions of l-AMN, isomerization into 2-AMN, and deacylation, which both increase the selectivity to the desired product 2-AMN were demonstrated to occur on BEA zeolites.1261 This is shown in Figure 3.4 on a HBEA-15 (framework Si/Al ratio of 15). After 45 min of reaction, AA is completely consumed, AMN and acetic acid being the only reaction products (yield in AMN with respect to AA close to 100%). Afterward there is a slow decrease in this yield indicating a deacylation process, and a faster increase in the 2- and 3-AMN... 

The location of 2-MN acetylation reactions over HBEA zeolites was widely debated. Some authors claim that the bulkier isomer 1-AMN can only be formed at the generally large external surface of BEA zeolite, the linear isomer 2-AMN both within the micropores and on the external surface 119,21,24,28,381 other authors state that both isomers are essentially formed within the micropores.[26,32,33,35] Both proposals can explain the increase in the selectivity to the bulky isomer (1-AMN) with decrease in the crystallite size/28 321 Indeed the smaller this size, the greater the external surface, hence the higher the rate of reactions on this surface, but also the shorter the micropore length and, consequently, the smaller the differences in the rates of desorption of the bulky and linear isomers. Both proposals can also explain the decrease in the selectivity for 1-AMN with the passivation or the poisoning of the external surface by bulky base molecules.[28] Additional arguments in favour of the formation of both isomers within the micropores are provided by ... 

The initial rate of 2-MN acetylation depends on the framework Si/Al ratio of the zeolite catalyst.[27] For a series of dealuminated BEA samples (by treatment with hydrochloric acid or with ammonium hexafluorosilicate), the acetylation rate passes through a maximum for a number of framework A1 atoms per unit cell (/VA() between 1.5 and 2.0 (Si/Al ratio between 30 and 40). The activity of the protonic sites (i.e. the TOF) increases significantly with Si/Al from 420 h 1 for Si/Al = 15 to 2650 h 1 for Si/Al = 90. It should be noted that similar TOF values could be expected from the next nearest neighbour (NNN) model. Indeed all the framework A1 atoms of the zeolite (hence all the corresponding protonic acid sites) are isolated for Si/Al ratio 10.5. Therefore the acid strength of the protonic sites is then maximal as well as their activity.[57,58] This was furthermore found for m-xylcnc isomerization over the same series of BEA zeolites.1271 This increase in TOF for... 

In the years since 1998, some papers have reported the benzoylation of substituted benzene derivatives, such as toluene, [9-11] ethyl benzene,[11] xylene,19 11 121 anisole/9 131 dimethoxybenzene,[14] biphenyl/151 phenol[16] and chlorobenzene1171 in the presence of zeolites and, in most cases, particularly H-BEA zeolite. 

Scheme 4.2 Benzoylation of o-xylene to 3,4-dimethylbenzophenone with benzoyl chloride over H-BEA zeolite.

The same effect is found for toluene acylation over BEA zeolite with derivatives of isobutyric acid isobutyric anhydride presents a higher initial activity compared with isobutyric chloride.[6]... 

For phenylbenzoate, the relatively more constrained H-BEA zeolite shows a much higher selectivity and an improved 4-HPB/2-HPB ratio (p/o = 2.1). Such a... 

Benzoylation of benzene and other aromatic compounds by benzoyl chloride over H-BEA zeolite modified by indium oxides has been investigated.191 We report in Table 4.2 the time required for half reaction (L/2) f°r a series of aromatic substrates used in the above reaction. The benzoylation reaction rate (via L /2 value) depends strongly on the substituent group present in the aromatic substrate and increases due to the presence of the electron-donating group, depending upon its electron-donating ability. The activity order is as follows benzene toluene < p-xylene < anisole. 

Figure 4.2 Hammett relationship (log 11/2 versus a) in the benzoylation reaction of benzene and substituted aromatic compounds with benzoyl chloride over H-BEA zeolite modified by indium oxides...

Barthel, N., Finiels, A., Moreau, C., Jacquot, R., Spagnol, M. Kinetic study and reaction mechanism of the hydroxyalkylation of aromatic compounds over H-BEA zeolites, J. Mol. Catal., A, 2001, 169, 163-169. 

Unfortunately, the use of TS1 (as well as TS2 discovered in 1990 by the group of Ratnasamy (27)) in catalytic oxidations is restricted to the relatively small substrates able to enter the pores of these zeolites (apertures 0.55 nm). Therefore, many research groups attempted to incorporate titanium in large pore molecular sieves BEA zeolites, mesoporous molecular sieves MCM41 and MCM48. Other transition metal zeolites were also synthesized and tested in oxidation one of the main problems of these systems is the release of redox cations in liquid phase (24). Progress remains to be made to develop molecular sieves catalyzing the oxidation... 

All these aspects were thoroughly discussed by lecturers and participants during the round table organized during the Poitiers School on The Future Trends in Zeolite Applications . Special emphasis was placed on the role played by the sites at the external surface (pockets, etc.) or at the pore mouth, by mesopores, extraframework aluminum species, as well as by the polarity of reactant and product molecules. Other important topics dealt with the remarkable catalytic properties of BEA zeolites for fine chemical synthesis, the potential of mesoporous molecular sieves, zeolitic membranes and the role of combinatorial catalysis in the development of zeolite catalysts. It is our hope that the fruits of these discussions will appear in the literature or even better as new and environmentally friendly products or processes. 

Fig. 3.3 Relationship between unit cell size and framework al content 3.2.2.2 MFI and BEA zeolite synthesis...

H. van Bekkum et al. (17) reported that the alpha-pinene oxide 9 can be succesfully converted to campholenic aldehyde 10 (Eq. 15.2.5) in the presence of a BEA-zeolite. Ti-BEA proves to be an excellent catalyst for the rearrangement of a-pinene oxide to campholenic aldehyde in both the liquid and vapor phase. This is mainly attributed to the presence of isolated, well-dispersed titanium sites in a Bronsted-acid-free silica matrix. Furthermore, the unique molecularsized pore structure of the zeolite may enhance selectivity by shape-selectivity. 

The addition of OMCTS to a BEA zeolite does not modify its 5xe(BEA) = 113 ppm, nor its line width, AH= 4.3 ppm for an equilibrium xenon pressure of 600 T, whatever the interval between the moment at which the OMCTS is added and the 129xe NMR spectrum recorded, up to 6 months later (Figure not shown). This observation indicates ... 

Roh et al.116 investigated the desulfurization of natural gas over AC, Fe/AC, BEA zeolite (BEA), and Fe/BEA for fuel cells. Sulfur capacities were obtained from... 

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