Zeolite lanthanum

Until the late 1970s, the NaY zeolite was mostly ion exchanged with rare earth components. Rare earth components, such as lanthanum and... 

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]. 

When rare earth Y-zeolite (REY) was added to the PILC or to the parent clay, the dried PILC or "as received" clay was reslurried in water and the calcined REY added to the 10 wt % level. This slurry was then mixed, filtered, dried, and calcined at 500 C for 2 hours in air. The calcined REY was obtained from Union Carbide and contained 14.1 wt % rare earth elements, primarily lanthanum and cerium. Portions of the PILC were pretreated by one of the methods listed below prior to the microactivity testing. 

Rare earth stabilization, as it relates to zeolite performance, has already been discussed. However, catalyst performance also varies depending on how the rare earths are deposited within the zeolite and the matrix, and also on how the ratio of individual species (such as lanthanum, cerium, and the other rare earths) are distributed. Yttrium can also be used to enhance zeolite catalyst performance and stability. These also seem to help mitigate the detrimental effect of vanadium, the most common and controversial contaminant. 

Nearly all the present work was done with Linde X and Linde Y zeolites, obtained from Union Carbide Corp. these were exchanged with one or two of the rare earths—yttrium, lanthanum, praseodymium, neo-... 

Tphe excellent catalytic activity of lanthanum exchanged faujasite zeo-A lites in reactions involving carbonium ions has been reported previously (1—10). Studies deal with isomerization (o-xylene (1), 1-methy 1-2-ethylbenzene (2)), alkylation (ethylene-benzene (3) propylene-benzene (4), propylene-toluene (5)), and cracking reactions (n-butane (5), n-hexane, n-heptane, ethylbenzene (6), cumene (7, 8, 10)). The catalytic activity of LaY zeolites is equivalent to that of HY zeolites (5 7). The stability of activity for LaY was studied after thermal treatment up to 750° C. However, discrepancies arise in the determination of the optimal temperatures of pretreatment. For the same kind of reaction (alkylation), the activity increases (4), remains constant (5), or decreases (3) with increasing temperatures. These results may be attributed to experimental conditions (5) and to differences in the nature of the active sites involved. Other factors, such as the introduction of cations (11) and rehydration treatments (6), may influence the catalytic activity. Water vapor effects are easily... 

It is unexpected that the catalytic activity and the proton acidity do not depend on the lanthanum content. This result cannot be related to the schemes of hydrolysis of the zeolitic rare earth cations reviewed in Ref. 13. On the other hand, acidity measurements in solution (15) have shown that in the lanthanum zeolites studied in this work the La3+ ions have replaced the NH4+ ions and have not formed a lanthanum compound (13). Finally, the variations in the sodium content of these lanthanum zeolites do not seem to be the dominant factor in contrast to the alkaline earth zeolites (26). 

Introducing 3.7 to 13.2 La3+ ions/unit cell in the Na-8.7 zeolites or 4 La3+ ions/unit cell in the D.Na-5.4 zeolite raises the thermal stability substantially. The lanthanum samples have the same activity after a 900°C pretreatment than after a 550°C pretreatment whereas the Na-8.7 material starts to lose its activity at 700° C. This high stability of polyvalent cationic zeolites has been reported previously in few studies but at temperatures lower than in our work (29, 80,31). 

Rehydration of the samples occurs even after a 900°C-pretreatment and gives rise to IR OH bands having the usual frequencies. It had been reported that rehydration of lanthanum zeolites heated at 700° C regenerated the catalytic activity (5). Therefore, the thermal stability of activity seems to be related to the rehydration. This rehydration of the lanthanum zeolites pretreated at 900° C leads to the formation of a significant number of acid sites of the same strength in regard to Py as those present on the 550°C-pretreated Na-8.7 zeolite rehydrated in the same conditions. 

Since heating conditions (32) and aluminum extraction leading to a high stability have been avoided, the increased stability of the catalysts seems related to the presence of exchanged lanthanum. A zeolite with high thermostability can be obtained by introducing only 3.7 La3+ ions/unit cell into a decationated zeolite. A higher content of lanthanum does not... 

As reported by Olmez and Gordon (University of Maryland), the concentration pattern of rare earth elements on fine airborne particles (less than 2.5 micrometers in diameter) is distorted from the crustal abundance pattern in areas influenced by emissions from oil-fired plants and refineries. The ratio of lanthanum (La) to samarium (Sm) is often greater than 20 (crustal ratio is less than 6). The unusual pattern apparently results from tlie distribution of rare earths in zeolite catalysts used in refining oil. Oil industry emissions have been found to perturb the rare earth pattern even in very remote locations, such as the Mauna Loa Observatory in Hawaii. 

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. 

Figure 3. Binary phase masks of equilibrium VGO catalyst images. a) particle location mask b) Si/Al intensity ratio c) high Si/Al ratio mask d) high lanthanum mask e) zeolite mask (logical AND of c d)...

The deactivation of a lanthanum exchanged zeolite Y catalyst for isopropyl benzene (cumene) cracking was studied using a thermobalance. The kinetics of the main reaction and the coking reaction were determined. The effects of catalyst coke content and poisoning by nitrogen compounds, quinoline, pyridine, and aniline, were evaluated. The Froment-Bischoff approach to modeling catalyst deactivation was used. 

The lanthanum exchanged Y zeolite (LaY) was made by contacting an ammonium Y (Linde type 31-200 powder) with an aqueous solution of lanthanum chloride. Approximately 60-70 percent of the ammonium ions were exchanged in the procedure. The resulting LaY powder was pressed into tablets, crushed and sieved to -60+80 mesh. 

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