Y zeolites preparation

ALUMINUM DEFICIENT Y ZEOLITES PREPARED BY STEAM/ACID TREATMENT (L8)a... 

It has already been mentioned that the formation of ultrastable Y zeolites has been related to the expulsion of A1 from the framework into the zeolite cages in the presence of steam (8,9), and the filling of framework vacancies by silicon atoms (11,12). This results in a smaller unit cell size and lower ion- exchange capacity (6). It also results in a shift of X-ray diffraction peaks to higher 20 values. Ultrastable Y zeolites prepared with two calcination steps (USY-B) have a more silicious framework than those prepared with a single calcination step (USY-A). Furthermore, since fewer aluminum atoms are left in the USY-B framework, its unit cell size and ion-exchange capacity are also lower and most of the nonframework aluminum is in neutral form (18). 

Thomas et al. (39,41) recorded the Si-NMR spectrum of an aluminum-deficient Y zeolite prepared by reacting NaY zeolite with SiCl vapors. The spectrum showed a single sharp peak, characteristic of Si(0 Al) groupings, and indicative of an essentially luminum-free faujasite structure. 

Aluminum-deficient Y zeolites prepared by reacting Y zeolites with SiCl vapors at 500°C also showed an enrichment of the surface in aluminum (44). The X-ray data show a shift of diffraction peaks to higher 20 values, consistent with a more silicious framework (27). However, the X-ray pattern also indicates some structural differences between this material and the one prepared by the steam/acid treatment. 

Stability. Ultrastable Y zeolites, prepared by the hydrothermal treatment of ammonium Y zeolites, have considerable thermal and hydrothermal stability (6) The high... 

Aluminum-deficient Y zeolites prepared by partial removal of aluminum with a chelating agent (e.g. EDTA) also show improved thermal and hydrothermal stability compared to the parent zeolite. The optimum stability was found in the range of 25 to 50 percent of framework A1 extraction (8). However, the maximum degree of dealumination is also affected by the SiO /Al O ratio in the parent zeolite a higher ratio appears to allow more advanced dealumination without loss of crystallinity (8,25,45). Above 50 or 60 percent dealumination, significant loss of crystallinity was observed. Calcination of the aluminum-deficient zeolite resulted in a material with a smaller unit cell size and lower ion-exchange capacity compared to the parent zeolite. 

The mid-infrared spectra of aluminum-deficient Y zeolites prepared by the reaction of Y zeolites with SiCl are similar to those prepared by steam/acid treatment (27). As in the... 

Catalysts containing aluminum-deficient Y zeolites prepared by Al extraction with chelating agents have been used for cracking and hydrocracking hydrocarbons, e.g. (100). 

XPS has been used, in quite a different context from its usual application in metal systems, by Defosse and Canesson " they studied the acidity of catalysts important in cracking, isomerization, and dehydration. They used a NH4-Y zeolite, prepared from Na-Y. Samples were activated by being heated in vacuum at temperatures between 20 and 900 °C. Pyridine was admitted to the samples at 20 °C and samples were transferred direct to the ESCA spectrometer. 

Strong Acid Sites of Dealuminated Y Zeolites Prepared by Conventional Treatments and Isomorphous Substitution... 

The acidity of dealuminated Y zeolites prepared either by conventional treatments or isomorphous substitution has been characterized in detail through a microcalorimetric study of the adsorption of ammonia. 

Materials. Zeolites A, X, Y, and L were from Union Carbide Corporation, and Zeolite Z was a synthetic large port mordenite from Norton Company. Chabasite was a crystallographically very pure natural zeolite from an Hungarian deposit. Zeolite Y is an aluminum-deficient Y zeolite prepared by H4EDTA treatment. The hexammine complex of was from Strem Chemicals. The ruthenium-on-alumina catalyst was from Ventron. 

A. Macedo, A. Auroux, F. Raatz, E. Jacquinot, R. Boulet et al.. Strong acid sites of dealuminated Y zeolites prepared by conventional treatments and isomorphous substitution. ACS Symp. Sen 368, 98-104 (1988)... 

Niobium and tantalum containing Y zeolites prepared via the one-pot synthesis showed the FAU stmcture, as evidenced by XRD diffraction patterns (Fig. 1 - the numbers in the symbols indicate the assumed Si/M ratio). The zeohte stmcture is confirmed for the two zeolites of both Si/M ratios (64 and 32) hence the synthesis of faujasite samples... 

Zhixiang et al. [107] compared typical characteristics of aliunimun-deficient Y zeolites prepared by steaming followed by add leaching and produced by the reverse sequence of the two steps. The sample obtained by the reverse method showed, in contrast to the other one, aluminum eiuichment on the external surface of the crystals and lower charge and add site density on the intracrystalline and mesopore surface. 

---