Dealuminated HY zeolites

The A1 NMR spectra of three steam-dealuminated HY zeolites are shown in Figure 1. They Sjt w one intense line centered at 60 ppm (tetrahedral aluminum, A1 ) d two more lines at ppm and 0... 

In heavily steam-dealuminated zeolites, most of the activity should come from the EFAL that is concentrated on the external siirface (3,4). We believe that Levyis acidity, which can stabilize radicals, can play an important role in the radical cracking observed with strongly steam-dealuminated HY zeolites. Furthermore,... 

Finally, the variation of the yields of gasoline and diesel versus A1 per unit cell allow us to conclude that highly steam-dealuminated HY zeolites behave, from the point of view of gas-oil cracking, like a well-dispersed active alumina. 

Monodirectional 12 membered ring zeolites (offretite, L, mordenite and 0) are very inefficient as catalysts for formaldehyde benzene condensation to give diphenylmethane, esterification of phenylacetio acid with equimolar amounts of ethanol, Friedel-Crafts acylation of 3-phenylpropanoyl chloride with anisole and Claisen-Schmidt condensation of acetophenone with benzaldehyde. This fact has been attributed to diffusional constraints of organic compounds inside the channels. By contrast, the behaviour of the tridireotional f zeolite is very similar to that of dealuminated HY zeolites, inoreasing the turnover of the acid sites with the framework Si-to-Al ratio. 

Meric, P., Finiels, A., Moreau, P. Kinetics of 2-methoxynaphthlene acetylation with acetic anhydride over dealuminated HY zeolites, J. Mol. Catal., A, 2002, 189, 251-262. 

Another effect of zeolite pore architecture on esterification is found in the lactonization of 15-hydroxypentadecanoic acid. With dissolved acid catalysts or with amorphous Si02-Al203, dimerization or polymerization are the dominant reactions, but when the reactant is adsorbed within the pores of a dealuminated HY zeolite, only the pentadecanolide is obtained (8) ... 

Figure 7) - 129-Xe NMR chemical shift as a function of sorbed Xe of dealuminated HY zeolites at 300 K. fresh sample 3% coked sample A 10.5% coked sample 15% coked sample, (reproduced with the permission from reference 24)...

Figure 9.16 Differential heats of ammonia adsorption versus coverage for dealuminated HY zeolites.

Figure 3 Coke formation during n-heptane cracking at 350°C over dealuminated HY zeolites.

FT—IR Study of the Bronsted Acid Sites in Dealuminated HY Zeolites Using Specific Probe Molecules... 

HT, HTA solids. It has been found that the l.f. band, in contrast to the h.f. one, is insensitive to pyridine in the case of non dealuminated HY zeolites (5,11) however, it tends to be sensitive after dealumination (5,11). In our case, the structural bands (h.f.,l.f.) disappear completely after pyridine adsorption whatever the physicochemical characteristics of the solids (figure 2). More surprising is the behaviour of the silanol band (3742 cm-1). While the low frequency part of it (3738 cm-1) appears to be insensitive to pyridine, the high frequency part (3743 cm-1) does interact with pyridine. This interaction persists even after evacuation at higher temperatures up to 723 K. Thus, two components are responsible for the silanol band. 

Parameters in Addition to the Unit Cell That Determine the Cracking Activity and Selectivity of Dealuminated HY Zeolites... 

The cracking activity and selectivity for n-heptane and gas-oil, of a series of dealuminated HY zeolites (SiCl4 or steam dealuminated) have been measured. The results have been related with the different types of aluminium and acid groups present and to the pore volume distribution. It is clearly shown that the unit cell parameter (framework Si/Al ratio) can not explain, by itself, the activity and selectivity of dealuminated zeolites. 

Moreover, the sharp changes in selectivity observed for samples with a0 below 24.24 X cannot be explained only on the bases of the strength and density of the acid sites. In order to explain those results, we must consider the different types of tetrahedral and octahedral extraframework aluminium as well as the texture and adsorption hydrophobicity characteristics of the zeolites. Finally, the existence of radical-type cracking, which becomes especially important on highly dealuminated HY zeolites, must be taken into account. 

With calcined samples, the spectra fall into three categories, represented on Figure 7a, b, c. The first kind of spectrum is found on zeolite Ni-, HY2 7 and shown on Figure 7a. The position of the three" bands indicates that nickel ions are again in octahedral coordination. They are likely to be stabilized at S- sites of the HY structure (14). The same type of spectrum is observed with all non dealuminated HY zeolites, and also at small nickel concentration over the mildly dealuminated HY15. However a splitting of the absorption near 15000 cm 1 and a weak additional band at 5000 cm-1 indicate that some nickel ions are located in sites with a symmetry lower than S- in the zeolite structure. 

Similar results were obtained by Chapat et al. [56] for the glucosidation of 1-butanol over a series of dealuminated HY zeolites with different framework Si/ Al ratios (2.5 to 100) under similar reaction conditions. From Table 5 it can be seen that for dealuminated HY zeolites the activity increases up to an Si/AI ratio of 15, and then decreases significantly. 

Cyclization. A macrocyclic lactone has been acquired (with yields up to 32%) from 15-hydroxypentadecanoic acid by exposure to dealuminated HY zeolite. Five-and six-merhbered heterocycles can be synthesized from diols with a modified ZSM-5 zeolite (from 18-30 mesh HZSM-5 and Cr20j, and activated at 420°C for 4 h). For example, IV-methylpyrrolidine is obtained in 64% yield from 1,4-butanediol and methylamine. ... 

Parameters in addition to the unit cell that determine the cracking activity and selectivity of dealuminated HY zeolite, in ACS Symposium Series, Vol. 368, eds W.H. Flank and T.E. Whyte (ACS, Washington, DC) pp. 542—554. 

The kinetic study of the acylation reaction of thiophene with acyl chlorides over dealuminated HY zeolites, in chlorobenzene as solvent, has been shown to follow a Langmuir-Hinshelwood type kinetic law. In liquid phase conditions, thiophene is slightly more adsorbed than the acyl chloride. Moreover, the study of the reaction with various substituted benzoyl chlorides X-CgH4-COCl shows that the nature of the substituent has very little influence on the initial rate. 

Dealuminated HY zeolites have been shown to be efficient catalysts for the selective preparation of 2-acyl thiophenes in the reaction nf thiophene with various acyl chlorides. The acylation reaction of thiophene with butyroyl chloride over HY (Si/Al =15) zeolite, in chlorobenzene as solvent, follows a Langmuir-Hinshelwood kinetic law, which involves the adsorption of the two reactants on identical sites of the catalyst surface. ... 

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