H-ZSM-5 zeolite

To explain how solid acids such as Nafion-H or HZSM-5 can show remarkable catalytic activity in hydrocarbon transformations, the nature of activation at the acidie sites of such solid acids must be eon-sidered. Nafion-H contains acidic -SO3H groups in clustered pockets. In the acidic zeolite H-ZSM-5 the active Bronsted and Tewis acid sites are in close proximity (—2.5 A). 

Vetyselecdve reducdon of nltroalkenes into the corresponding nitroalkanes is achieved using NaCNBH- in the presence of the zeolite H-ZSM 5 in methanol fEq. 3.48. ... 

Zeoliltes seem particularly suited to take over the job and in fact are doing so already for aromatic alkylation. Thus in ethylbenzene manufacture (from benzene and ethene) modern processes apply zeolites (H-ZSM-5, H-Y) as the catalyst, substituting conventional processes based on AICI3 or BF3-on-alumina catalysis. Substantial waste reductions are achieved. 

Temperature Programmed Desorption (TPD). Chemisorbed molecules are bonded to the surface by forces dependent on the nature of the sites. For instance, ammonia will be strongly adsorbed on acid sites, whereas it is only weakly adsorbed on basic sites. Consequently, the adsorbate complex formed with the basic sites will decompose at lower temperatures than that formed with the acid sites. The following example regarding the NH.i-zeolite H-ZSM-5 system will illustrate this. 

The water-insoluble salts such as Cs2,5Ho., iPWi204o efficiently catalyse dehydration of 2-propanol in the gas phase and alkylation of m-xylene and trimethyl benzene with cyclohexene this catalyst is much more active than Nafion-H, HY-zeolite, H-ZSM-5, and sulphated zirconia (Okuhara et al., 1992). 

As an example, Figure 3.1.10 illustrates the use of this procedure for elucidating the location of coke deposits on zeolite catalysts [62]. Samples of zeolites H-ZSM-5... 

DRIFT spectroscopy was used to determine Av0h shifts, induced by adsorption of N2 and hexane for zeolite H-ZSM-5 (ZSM-a and ZSM-b, Si/Al=15.5 and 26), H-mordenite (Mor-a and Mor-b, Si/AI— 6.8 and 10) and H-Y (Y-a and Y-b, Si/Al=2.5 and 10.4) samples. Catalysts were activated in 02 flow at 773 K in situ in the DRIFTS cell and contacted than with N2 at pressures up to 9 bar at 298 K or with 6.1% hexane/He mixture at 553 K, i.e., under reaction conditions. Catalytic activities of the solids were measured in a flow-through microreactor and kapp was obtained as slope of -ln(l-X0) vs. W/F plots. The concentration of Bronsted acid sites was determined by measuring the NH4+ ion-exchange capacity of the zeolite. The site specific apparent rate constant, TOFBapp, was obtained as the ratio of kapp and the concentration of Bronsted acid sites. 

Fig. 7 Hf Al REAPDOR analyses of bare zeolite H-ZSM-5 (a, b) and a 1 1 methanol loaded H-ZSM-5 (c, d). Adapted from [238] and [236] with permission from Elsevier...

Z-4A), and zeolite H-ZSM-5. The interlayer distance varied by the intercalation was determined from X-ray diffraction patterns. The interlayer space of the crystalline zeolite is separated by the three-dimensional cage structures. The mean diameters of particles were approximately 1 ym. Such small particles formed very stable suspensions with no sign of sedimentation over the time course of the kinetic measurements. The analytical techniques used to obtain the equilibrium concentration are described elsewhere (10-22). All samples were equilibrated for 24-72 h after preparation. The temperature was controlled at 25 °C. 

The location of p-xylene in a single crystal of zeolite H-ZSM-5 with a new, sorbate-induced, orthorhombic framework symmetry. Acta Crystal., B45, 423 31. 

Svelle, S., Joensen, F., Nervlov, J., Olsbye, U., lillerud, K.-P., Kolboe, S., and Bjorgen, M. (2005) Conversion of methanol into hydrocarbons over the zeolite H-ZSM-5 ethene formation is mechanistically separated from the formation of higher alkenes. /. Am. Chem. Soc., 128,14770-14771. 

Conversion of methanol to hydrocarbons over zeolite H-ZSM-5 on the origin of the olefinic species. 

Let us compare M-ZSM-5 zeolites with M = H+, Li+, Na, K+, Rb, Cs, AF+, on one hand, and organic electron donors of variable ionization potentials, on the other. Zeolite H-ZSM-5 generates cation-radicals from substrates with an oxidation potential of up to 1.65 V (Ramamurthy et al. 1991). The naphthalene sorption by Al-ZSM-5 zeolites calcified in an atmosphere of oxygen or argon leads to the appearance of two occluded particles—the naphthalene cation-radical and isolated electron. Both particles were fixed by ESR method. Back reaction between the oppositely charged particles proceeds in an extremely slow manner and both the signals persist over several weeks at room temperature (Moissette et al. 2003). 

Using acyl nitrates as nitrating agents (compare with Section 4.5.4.2) and zeolite H-ZSM-11 treated with tributylamine, Nagy et al. (1991, 1994) were able to nitrate toluene with an even more impressive percentage of the isomers obtained—ortho 2-3%, meta 1-2%, and para 95-98%. 

Frequently substantially more than catalytic amounts of a Lewis acid metal halide are required to effect Friedel-Crafts alkylation. This is due partly to complex formation between the metal halide and the reagents or products, especially if they contain oxygen or other donor atoms. Another reason is the formation of red oils. Red oils consist of protonated (alkylated) aromatics (i.e., arenium ions) containing metal halides in the counterions or complexed with olefin oligomers. This considerable drawback, however, can be eliminated when using solid acids such as clays,97 98 zeolites (H-ZSM-5),99,100 acidic cation-exchange resins, and perfluoro-alkanesulfonic acid resins (Nafion-H).101-104... 

Fig. 36. 27A1 MAS NMR spectra of zeolite H-ZSM-5 at three magnetic field strengths (15) The spectra of hydrated materials represent the following number of FID s (from top to bottom)-10,000, 130,000, and 350,000 while the spectra of the dehydrated materials needed 250 000 and 180,000 FID s. At 15.6 MHz no signal was obtained for the dehydrated material after 750 000 FID s.

Scholle et al. (197, 198) used H MAS NMR to study the acidity of the hydroxyl groups in zeolite H-ZSM-5 and its borosilicate equivalent, known as H-boralite, at various water contents. They were able to distinguish terminal and water hydroxyls from acidic hydroxyl groups in the framework, although the resolution of their spectra was lower than that achieved by the... 

The rearrangement of styrene oxide into phenyl acetaldehyde was studied over various zeolites (H-ZSM-5, HY, H-offretite). It was first shown that both external and internal acidic sites are involved in that easy isomerization. Moreover, a comparative study of the rearrangement of this epoxide and of its hindered analog, 1-phenyl-1,2-epoxycyclohexene, on silanated offretite, allowed a discrimination between the activities of these sites. 

Ikeda, T., Sasaki, M., and Yasunaga, T. (1984b). Kinetic studies of ion exchange of NH7 in zeolite H-ZSM-5 by the chemical relaxation method. J. Colloid Interface Sci. 98, 192-195. 

Figures 1A and 1B show the adsorption isotherms of xenon on the Na, H-ZSM-5 and H-ZSM-5 zeolites, respectively. From the comparison, one sees that xenon uptake decreases slightly (about 10%) with coke content in the Na, H-ZSM-5 with a low (1%) coke content, on zeolite H-ZSM-5, and decreases only slightly more with heavy coking (12%).

NMR/UV-vis Conversion of methanol to cyclic compounds on weakly dealuminated zeolite H-ZSM-5 [51]... 

Hunger M, Wang W. Formation of cyclic compounds and carbenium ions by conversion of methanol on weakly dealuminated zeolite H-ZSM-5 investigated via a novel in situ CF MAS NMR/UV-Vis technique. Chem Commun. 2004. 

Three different zeolites (USY-zeolite, H-ZSM-5 and H-mordenite) were investigated in a computer controlled experimental equipment under supercritical conditions using the disproportionation of ethylbenzene as test reaction and butane or pentane as an inert gas. Experiments were carried out at a pressure of 50 bar, a flow rate of 450 ml/min (at standard temperature and pressure), a range of temperatures (573 - 673 K) and 0.8 as molar fraction of ethylbenzene (EB) in the feed. The results showed that an extraction of coke deposited on the catalysts strongly depends on the physico-chemical properties of the catalysts. Coke deposited on Lewis centres can be more easily dissolved by supercritical fluid than that on Brnsted centres. 

H. van Koningsveld, J. C. Jansen, and H. van Bekkum, Zeolites, 10, 235 (1990). The Monoclinic Framework Structure of Zeolite H-ZSM-5. Comparison with the Orthorhombic Framework of As-Synthesized ZSM-5. 

The zeolite H-Y 92 containing 8% of the original content of Na" " cations was prepared by a repeated exchange of a sample of Na-Y (Si/Al=2.6) in an aqueous solution of NH4NO3 followed by calcination by Dr. J. Meusinger. For the zeolite H-ZSM-5 (Si/Al =17) the template-free synthesis and the transformation into the hydrogen form were performed by Dr. W. Schwieger [3]. 

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