La-Y zeolites

An interesting drop in selectivity from 10 to 0%, which parallels the increase in the concentration of electron-deficient species (Pt, Pt ), was observed in the series Pt-Na- Pt-Ca-, Pt-La-Y zeolites. This decrease in selectivity could mean, whatever the reaction mechanism adopted for hydrogenolysis and isomerization, that the former reaction requires more electron-deficient centers than the latter. 

Finally, La-Y zeolites were obtained by solid-state ion exchange between LaCl3 and the sodium form of Y-type zeolites as well [25]. This was proven by chemical analysis, IR, X-ray diffraction (XRD) and a test reaction. Details of the preparation and characterisation are outlined in Ref. [25]. Chemical analysis gave evidence for a partial replacement of sodium by lanthanum cations. IR showed the formation of acidic OH groups. Finally, XRD demonstrated, via the appearance of reflections of crystalline NaCl, that obviously Na cations were expelled from the interior of the zeolite crystals by in going La. Outside the zeolite particles they had formed small NaCl crystallites. 

A comparative study between the catalytic properties in the alkylation of isobutane and the changes of Bronsted acid sites by IR spectroscopy on Ce,La-Y zeolites (with Ce/La ratios from 0.75/0.25 to 0.25/0.75) has been carried out (Gardos et al. 1984). It was observed that the Ce/La distribution does not modify the catalytic behaviour of Ce,La-Y zeolites. In addition they observed that the IR absorption band at 3630 cm-1 can be related to the acidic OH groups responsible for the catalytic activity in the alkylation of isobutane with 1-butene. 

The formation of Ru(I)(CO)3 after activation of [Ru(NH3)g] in mordenite or in a deep-bed calcined La-Y zeolite under CO atmosphere at T<373 K was suggested through transmission FTIR spectroscopy in a contribution to this field of research by Schoonheydt et al. [619]. These authors observed bands at 2055,2005 and 1960 cm which were ascribable to Ru(I)(CO)3. However, they did not exclude the possibility that the spectral features could originate from a mixture of monocarbonyls (2005 and 1960 cm ) and dicarbonyls (2055 cm" ). 

Another substantial body of work dealing with cracking reactions has been reported over the past several years by Wojciechow-ski and coworkers. Results with cumene cracking over La-Y zeolite catalyst are summarized in entry 9 of Table 3. Catalyst deactivation in these studies is also treated as separable, but an hyperbolic function of time on stream is used for correlation of activity. The use of this type of correlation for a number of applications was summarized in a 1974 review (70). Since that time, in addition to recent work on cumene cracking (69) the model has been applied to an extensive series of studies on the cracking of gas oil distillates (71,72,73,74), as well as being employed in the correlation of Jacobs, et al. (77). 

Large-pore zeolites such as Y zeolites are efficient for the hydroamination of several olefins. For example, propene reacts with NH3 over SK-500 (a pelleted lanthanum-exchanged zeolite) or La-Y or H-Y zeolites with 6-15% conversion to give i-PrNHj with high selectivity (95-100%) (Eq. 4.5) [50]. 

The shape selectivity of zeolites is influenced by the location and distribution of charge-compensating cations. The charge-compensating ions other than protons are all quadrupolar. and Li NMR spectra of dehydrated LiX-1.0 identified three crystallographically distinct sites [221]. In the case NaX with Si/Al ratio of 1.23, six distinct sodium sites were identified using fast Na NMR, DOR and nutation techniques [222]. Na MQMAS has been extensively studied for zeolites X and Y [155]. Other cations like Cs and La in zeolites have also been investigated [155,... 

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. 

The distribution of cations in Na-Y, La,Na—Y and Cs,Na—Y zeolites were studied using xenon adsorption isotherms and Xenon- 129 NMR spectroscopy. 

Cs,Na-Y and La,Na—Y zeolites. The results are comparable with that of the Si and Na NMR investigations and the known structure data. 

A binder—free Na-Y zeolite with Si/Al ratio of 2.29 was obtained from Strem Chemical Co., La,Na—Y and Cs,Na-Y zeolites were prepared by exchanging Na-Y zeolite with LaCls and CsCl solution at room temperature. The percentage of metal ion exchanged in a zeolite has been determinated by Inductively-Coupled-Plasma Atomic Emission Spectroscopy and the number is used as prefix for the samples, e.g., Cs exchanged level of 667. is represented as 66Cs,Na-Y sample. 

The ESR spectrum observed when TNB was adsorbed on metal-exchanged Y zeolite was essentially a singlet (Co-, Ni-, La-exchanged) or a singlet with additional hyperfine structure (Ca exchanged). These systems are being further investigated. 

Hopkins (161) found that a steady decrease in n-heptane cracking activity occurred over La- and Ca-exchanged Y zeolites as the catalyst calcination temperature was increased from 350° to 650°C. The lanthanum form was about twice as active as the calcium form. Reduction in activity with increasing activation temperature was attributed to removal of acidic framework hydroxyl sites as dehydration becomes more extensive. The greater activity of La—Y with respect to the calcium form was thought to result from the greater hydrolysis tendency of lanthanum ion, which would require more extensive dehydration to result in the same concentration of acidic OH groups as found on Ca—Y. 

Sanple Preparation. Copper Y zeolite was prepared by ion exchange of sodium Y (Linde SK-40) zeolite with aqueous Cu(N03)2 solution. CuigNa24Y(Cu Y) (11) was obtained by stirring a slurry of 50g of NaY in 1 dm of 0.1 M Cu Oj at 25° for 4 h. The copper content was determined by spectrophotometry of Cu + after dissolution of exchanged sieve. The Cu Y zeolite was washed, air dried, and 2g samples were dehydrated in an apparatus (Fig. la) under vacuum first at room temperature and then at 100°C, 200°C, 300°C, and 400°C, being held at each temperature for one hour. 

The similarities in the Na cation distributions between the (NH, Na), (Ca,Na) and (La,Na) mixed cation systems in hydrated Y zeolites can be best demonstrated by comparing the sodium-23 MASNMR spectra at cation exchange levels where the NMR lines from the Na cations in the supercages and smaller cages are best resolved. For the (NH, Na), (Ca,Na) and (La,Na) cation systems these occur at exchange levels of 41, 45, and 52%, respectively. 

A different behaviour is observed for the dehydrated (Ca,Na) and (La,Na) cation systems. For these cation systems, dehydration of the Y zeolite is known to result in Ca or La penetration into... 

Sodium-23 MASNMR measurements have been used to examine the extent to which this method can be used to determine the cation distribution in hydrated and dehydrated Y-zeolites. Results have been obtained on Na-Y and series of partially exchanged (NH, Na)-Y, (Ca,Na)-Y and (La,Na)-Y zeolites which demonstrate that the sodium cations in the supercages can be distinguished from those in the smaller sodalite cages and hexagonal prisms. For the hydrated Y zeolites, spectral simulation with symmetric lines allows the cation distribution to be determined quantitatively. 

P. E. Eberly, Jr. (Esso Research Laboratories, Baton Rouge, La. 70821) In evaluating diffusivities, one frequently finds that the parameters D and interact. Thus, by changing M, one can affect the value of D. In your results comparing the various forms of Y zeolite, could changes in have affected the diffusivity values ... 

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