Zeolite catalysts rare earth

It is well known that incorporation of rare earth cations can greatly improve the hydrothermal stability of Y zeolite. Shu et al. have reported the incorporation of rare earth ions into the ZSM-5 structure by a seeding method in which an REY zeolite is dispersed in a gel containing Si-, A1-, Na- sources and water and the mixture converted into an MFI type zeolite. The resulting ZSM-5 zeolite containing rare earth ions was further modified under hydrothermal conditions and the final catalyst, denoted ZRP-1, has outstanding hydrothermal stability as shown in Table 3. 

The development of ultrastable Y-zeolite catalyst led to the production of gasoline with higher olefin content and increased octane niunber. However, the need for improved catalysts continued because the zeohte was not sufficiently stable and the motor octane number did not rise as much as the research octane number. As discovered previously with other zeolites in the 1960 s, partial exchange of USY-zeolite with rare earth (REUSY) gave better stability as well as activity and provided more branched hydrocarbons and aromatics. Both motor octane number and gasoline production could thus be increased. 

The alumina content, the amount of rare-earth, and the type and amount of zeolite affect catalyst tolerance to vanadium poisoning. 

A freshly manufactured zeolite has a relatively high UCS in the range of 24.50°A to 24.75°A. The thermal and hydrothermal environment of the regenerator extracts alumina from the zeolite structure and, therefore, reduces its UCS. The final UCS level depends on the rare earth and sodium level of the zeolite. The lower the sodium and rare earth content of the fresh zeolite, the lower UCS of the equilibrium catalyst (E-cat). 

UCS, rare earth, and sodium are just three of the parameters that are readily available to characterize the zeolite properties. They provide valuable information about catalyst behavior in the cat cracker. If required, additional tests can be conducted to examine other zeolite properties. 

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... 

Rare Earth is a generic name used for the 14 metallic elements of the lanthanide series used in the manufacturing of FCC catalyst to improve stability, activity, and gasoline selectivity of the zeolite. 

The ammonia is released and the protons remain in the zeolite, which then can be used as acidic catalysts. Applying this method, all extra-framework cations can be replaced by protons. Protonated zeolites with a low Si/Al ratio are not very stable. Their framework structure decomposes even upon moderate thermal treatment [8-10], A framework stabilization of Zeolite X or Y can be achieved by introducing rare earth (RE) cations in the Sodalite cages of these zeolites. Acidic sites are obtained by exchanging the zeolites with RE cations and subsequent heat treatment. During the heating, protons are formed due to the autoprotolysis of water molecules in the presence of the RE cations as follows ... 

Characterization techniques continue to develop and will impact their application to zeolitic systems. Aberration corrected electron microscopes are now being used to improve our understanding of catalysts and other nano-materials and will do the same for zeolites. For example, individual Pt atoms dispersed on a catalyst support are now able to be imaged in the STEM mode [252]. The application of this technique for imaging the location of rare-earth or other high atomic number cations in a zeolite would be expected to follow. Combining this with tomography... 

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... 

Different procedures can be used in practice to activate the zeolite, and the choice of a particular method will depend on the catalytic characteristics desired. If the main objective is to prepare a very active cracking catalyst, then a considerable percentage of the sodium is exchanged by rare earth cations. On the other hand, if the main purpose is to obtain gasoline with a high RON, ultrastable Y zeolites (USY) with very low Na content are prepared. Then a small amount of rare earth cations is exchanged, but a controlled steam deactivation step has to be introduced in the activation procedure to obtain a controlled dealumination of the zeolite. This procedure achieves a high thermal and hydrothermal stability of the zeolite, provided that silicon is inserted in the vacancies left by extraction of A1 from the framework (1). The commercial catalysts so obtained have framework Si/Al ratios in the... 

Rare Earths and Alumina. A much easier and cheaper way of getting the SO2 removal enhancement from rare earths that was observed with the well-exchanged rare earth Y zeolite was to add rare earths, especially cerium, by direct impregnation to high alumina cracking catalyst (24). 

---