Zeolites rare-earth-exchanged

Zeolites with lower UCS are initially less active than the conventional rare earth exchanged zeolites (Figure 3-5). However, the lower UCS zeolites tend to retain a greater fraction of their activity under severe thermal and hydrothermal treatments, hence the name ultrastable Y. 

A fully rare-earth-exchanged zeolite equilibrates at a high UCS. whereas a non-rare-earth zeolite equilibrates at a very low UCS in the range of 24.25 [3]. All intermediate levels of rare-earth-exchanged zeolite can be produced. The rare earth increases zeolite activity and... 

Figure 3-5. Comparison of activity retention between rare-earth-exchanged zeolites versus USY zeolites. (Source Grace Davison Octane Handbook.)...

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... 

The Future Role of Rare Earth Exchanged Zeolites in Catalytic Cracking ... 

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. 

In this case less of the rare earth exchanged zeolites would be required. 

Ward measured the o-xylene isomerization activities of Na, Mg, RE, and H—Y zeolites and found the rare earth form to be intermediate in activity between the magnesium and hydrogen forms as shown in Table IX (212). The sodium form was essentially inactive. He interpreted the activity relationship RE—Y > Mg—Y to result from the formation of two acidic structural hydroxyl groups per trivalent rare earth cation. The formation of acidic structure hydroxyl groups by exchange of sodium ions with protons in the rare earth solution, as proposed by Bolton (218), may also account for the greater activity of the rare earth-exchanged zeolite. 

According to this concept, Masuda et al. [75] studied the catalytic cracking of the oil coming from a previous thermal pyrolysis step of polyethylene at 450°C in the bench-scale fixed-bed reactor shown in Figure 3.11. The catalysts employed were different zeolite types REY (rare earth exchanged zeolite Y), Ni-REY (nickel and rare earth... 

The rare earth exchanged zeolites (LaHY, LaHB) and meso porous silica-alumina (2-4 nm diameter pores) were prepared previously [5], The unit cell composition of LaHY is (H Na, La,4Al52 Si,3940384). MSA is in the acid form, Si/Al = 50. The adsorption isotherm for LaHY yields a maximum of ca. 4 isobutane molecules per supercage (or 0.6 molc./Al). Triflic acid (Aldrich) was manipulated under dry nitrogen atmosphere. 

Since a large number of organic reactions were found to be catalyzed by rare earth-exchanged zeolites (Section III) a discussion of their properties is included. 

Selective Oxidation of Cyclohexane over Rare Earth Exchanged Zeolite Y... 

To establish the effect of hydrothermal treatment upon the rare earth exchanged zeolites, portions of these zeolites were steamed at different temperatures under 100% steam, and characterized by different physical methods. 

An early, non-shape-selective, application of zeolites in the Fischer indole synthesis was reported by Venuto and Landis [18]. They employed calcium-and rare-earth-exchanged zeolite X as catalysts under continuous-flow conditions at 150 °C. Good yields of indoles were obtained with both acetone and cyclohexanone phenylhydrazones a 72.5% yield of indole was obtained from the latter with CaX catalyst. 

Gauthier et al. (1989) studied the activity of various cation-exchanged Y-type zeolites in the acylation of toluene with octanoic acid, obtaining selectivities to the para isomer of 94% at 75% yield of acylated product. The most efficient catalysts were rare-earth-exchanged zeolites (70% exchange), the following order of activity being observed Cr3+, Zr4+ < M2+, Cu2+, Co2+ <11 < Pr3+, La3+, Gd3+, Yb3+, Ce3+. 

Iyer, ES., J. Scherzer and Z.C. Mester, 1988, 29Si and 27 A1 Magic angle spinnmg-NMR spectroscopy study of rare-earth-exchanged zeolites, in Perspectives in Molecular Sieve Science, eds W.H. Flank and T.E. White, Vol. 368 of ACS Symposium Series (American Chemical Society, Washington, DC) pp. 48-65. 

Pires, E.L., M. Wallau and U. Schuchardt, 1997, Selective oxidation of cyclohexane over rare earth exchanged zeolite Y, in 3rd World Congr. on Oxidation Catalysis, eds R.K. Grasselli, S.T. Oyama, A.M. Gaflhey and J.E. Lyons, Vol. 110 of Studies in Surface Science and Catalysis (Elsevier, Amsterdam) pp. 1025-1027. 

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