Rare-earth-exchanged catalysts

At this state of the catalyst synthesis there are two approaches for further treamient of NaY. Depending on the particular catalyst and the catalyst supplier, further treatment (rare earth exchanged) of NaY can be accomplished either before or after its incorporation into the matrix. Post-treatment of the NaY zeolite is simpler, but may reduce ion exchange efficiency. 

A rare-earth-exchanged zeolite increases hydrogen transfer reactions. In simple terms, rare earth forms bridges between two to three acid sites in the catalyst framework. In doing so, the rare earth protects... 

In the early 70 s, FCC formulations containing 10-40% CREY (calcined rare-earth exchanged Y zeolites) were widely employed because these catalysts offered improved chemical as well as thermal and hydrothermal stability over FCC compositions containing equivalent amounts of (low sodium) HY crystals (23-25). The... 

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... 

The curve shown for 60% AI2O3 actually represents two catalysts one with and one without rare earth exchange. At first, the similarity of these two catalysts underestimated the importance of rare earth content. 

Rare-earth exchanged [Ce ", La ", Sm"" and RE (RE = La/Ce/Pr/Nd)] Na-Y zeolites, K-10 montmorillonite clay and amorphous silica-alumina have also been employed as solid acid catalysts for the vapour-phase Beckmann rearrangement of salicylaldoxime 245 to benzoxazole 248 (equation 74) and of cinnamaldoxime to isoquinoline . Under appropriate reaction conditions on zeolites, salicyl aldoxime 245 undergoes E-Z isomerization followed by Beckmann rearrangement and leads to the formation of benzoxazole 248 as the major product. Fragmentation product 247 and primary amide 246 are formed as minor compounds. When catalysts with both Br0nsted and Lewis acidity were used, a correlation between the amount of Br0nsted acid sites and benzoxazole 248 yields was observed. 

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. 

What about the future Like many other industries, catalyst manufacturers are dependent on refinery requirements and crude oil availability. Although crude oil supplies may become limited and catalyst usage reduced, rare earth usage in cracking catalyst may be unaffected. This is because crudes that are likely to be processed are expected to be more difficult to crack requiring higher stability and activity and thus more rare earth exchanged zeolite pef unit of catalyst. 

A rare-earth-exchanged Y (REY) zeolite was used as the catalyst in all the runs here. The zeolite was donated by W.R. Grace and Co. Some properties of the catalyst are given in Table I Cumene, obtained from Aldrich Chemicals, was used as the base-case reactant. Naphthalene, from Fisher Scientific, and decane, from Aldrich Chemicals were added in various proportions as coking agents. All reactants were at least 99% pure and were used as received. 

Simultaneously scientists at Esso Research and Engineering and Mobil Oil were working with X based catalysts [33-35]. Mobil Oil introduced the first zeolite based catalysts for cracking gas oils in 1962 using rare earth exchanged X in a silica-alumina matrix. This replaced the older silica-alumina catalysts. When we made Y available, the Y based catalysts largely replaced the X based catalysts in this application. 

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