Zeolite, lanthanum exchanged preparation

In the case of cerium exchanged zeolites, the ionic exchanges were carried out under nitrogen, in order to avoid the oxidation of cerium (III) ions. Part of the cerium (III) exchanged zeolite was calcined under oxygen for 6 hours at 540°C in order to convert cerium (III) to cerium (IV) ions. Lanthanum-cerium exchanged zeolites were prepared with the following composition 75% La, 25% Ce 50% La, 50% Ce and 25% La, 75% Ce. 

Lanthanum is known to improve the hydrothermic stability of Y-type zeolites [20]. A second attempt to stabilize the catalyst was made by preparing La-exchanged EMT-type samples. The dealumination process was stopped but this catalyst did not present any catalytic activity in NO reduction. A La-Cu-EMT-3.8-70-10 sample was also prepared. A maximum extent of reduction of 15% was measured at 500°C. This low activity in NO reduction is probably due to the very low copper content. 

Lanthanum (La), cerium (Ce), praseodymium (Pr) and neodymium (Nd) exchanged Y zeolites with different rare earth content, as well as mixed lanthanum-cerium exchanged. eolites, taute been prepared and characterized. sSi and 7A1 MASNMR spectra, surface area, crystallinity and unit cell size data were obtained for fresh and steamed zeolites. The stability of these zeolites toward steam has been investigated. An increase in lanthanum content from about 14 wt% La 03 to over 20 wt% enhances the stability of the Lar zeolite towards dealumination by steam. A similar effect was observed >r NdY and PrY zeolites. The resolution loss of Si- JR sigqia 1 s observed for paramagnetic jpns (Nd3, Pr, ... 

In their use as catalyst components, rare earth Y zeolites are freauently prepared by ion exchange with commercial rare earth salt solutions. Such commercial salts are mixtures of different rare earths, in which the major components are lanthanum, cerium, praseodymium and neodymium (5). These rare earth elements therefore play a major role in determining the physico-chemical characteristics and stability of Y zeolites that are used in many commercial catalysts. 

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. 

Karge, H.G., G. Borbely, H.K. Beyer and G. Onyestyak, 1988a, Solid-state ion exchange in zeolites. Part HI. Preparation and test of lanthanum zeolite catalysts, in Proc. 9th Int. Congress on Catalysis, Ottawa, 1988, eds M.J. Phylips and M. Teman (The Chemical Institute of Canada, Ontario) pp. 396-403. 

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