Rare earth exchanged faujasites

Table III compares the gasoline composition from three steam deactivated catalyst systems. The first contains 10% rare earth exchanged faujasite (RE FAU) in an inert silica/clay matrix at a cell size of 2.446 nm the second contains 20% of an ultra stable faujasite (Z-14 USY) at a unit cell size of 2.426 nm in inert matrix. The third contains 50% amorphous high surface area silica-alumina (70% AI2O3 30% Si02) and 50% clay the nitrogen BET surface area of this catalyst after steam deactivation is 140 m /g. All three catalysts were deactivated for 4 hrs. at 100% steam and at 816°C.

The increase in octane observed using dealuminated faujasite compared to high cell size rare earth exchanged faujasite has been correlated with the Si/AI ratio of the sieve and with the sodium content (3). While the relationship between Si/Al ratio as measured by unit cell is confirmed by pilot unit studies in our laboratory. Figure 1, the relationship with sodium content is more complicated. Figure 2. Sodium added to the catalyst after hydrothermal dealumination reduces activity but does not affect octane, while sodium present before hydrothermal dealumination increases activity but does reduce octane. This result implies that selectivity for octane is related to structures formed during... 

An inspection of the industrial use of zeolites as catalysts shows, however, that only a rather limited number of zeolite topologies are currently used in major industrial processes. Among the more important ones are ultrastable Y (USY) (FAU), rare-earth-exchanged faujasite-type (X, Y) (FAU) andZSM-5-type (MFI) zeolites in fluid catalytic cracking (FCC) of oil fractions [4] noble-metal-loaded U SY for hydroisomerization and hydrocracking of naphtha feedstocks [5] mordenite (MOR) and zeolite Omega (MAZ) -based catalysts for C4-C6 alkane isomerization [6] zeolites ZSM-23 (MTT), ZSM-35 (FER), ZSM-5 for selective oil dewaxing [7] ZSM-5, silicalite (MFI), MCM-22 (MWW), Beta-type (BEA) zeolites for aromatics alkylation to yield ethylbenzene, p-xylene. 

Hydrothermal (steam) stability is also important, in as much as the catalyst must pass through a high temperature stripping zone in which the usual fluid stripping medium is steam. In our laboratory, zeolite hydrothermal stability is measured by comparing the x-ray crystallinity of the unknown faujasite sample with that of a fully rare earth exchanged reference standard following a 3 hour, 100% steam, 1500 F treatment. 

R-USY correspond to metal- and rare-earth-exchanged material X Zeolite with faujasite structure, a... 

There are many works on the alkylation of isobutane with olefins by using faujasite-type zeolites, especially rare-earth exchanged varieties. The recent progress in this field is comprehensively summarized by Weitkemp. In general, although zeolites are initially very active, they undergo rapid deactivation. 

Figure 11 shows that maximum hydrothermal stability for this faujasite was obtained a rare earth oxide level of only 7 Wt.%. However, since maximum thermal stability was achieved at abou the 20% rare earth oxide level, the exchange should be carried out to the 20% level in order to maximize overall stability characteristics. 

The structure of and possible cation location in these materials is fairly well known (2, 8, 4, )> and their ion-exchange behavior toward a multitude of pairs of ions, mostly including sodium, has been measured and interpreted in terms of basic properties of ions, crystal structures, and pore dimensions. The major part of these studies is with alkali- and alkaline-earth cations, alkylammonium ions, rare-earth cations, and silver and thallium ions (1). In contrast, the ion adsorption of transition metals in faujasite has received little attention. 

Information published during thepast few years about the faujasite class of zeolites indicated that they present a possibly unique system in which the necessary conditions might be met. Sherry (4, 5) reported that rare earths, as compared with alkali or alkaline earth metals, are readily exchanged into Linde X from dilute aqueous solutions, and that they strongly favor the zeolite phase. When such an exchanged zeolite is dehydrated by heating to 350-700° C, the lanthanide ions move into the small pore system (6>, 7) after which they are not readily exchanged back out of the crystal. Smith (8) has reviewed the structure of lanthanide X and Y zeolites. 

Infrared spectral studies of rare earth (RE) ion-exchanged faujasites have been reported by Rabo et al. (214), Christner et al. (217), Ward (211, 212), and Bolton (218). Distinct hydroxyl absorption bands are observed at 3740, 3640, and 3522 cm-1 after calcination at temperatures in the range of 340° to 450°C. As previously discussed, the hydroxyl groups at 3740 cm-1 are attributed to silanol groups either located at lattice termination sites or arising from amorphous silica associated with the structure. The hydroxyl groups that form the 3522 cm-1 band are nonacidic to pyridine or piperidine and are thought to be associated with the rare earth cations. 

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