Of dealuminated zeolites

In view of catalytic potential applications, there is a need for a convenient means of characterization of the porosity of new catalyst materials in order to quickly target the potential industrial catalytic applications of the studied catalysts. The use of model test reactions is a characterization tool of first choice, since this method has been very successful with zeolites where it precisely reflects shape-selectivity effects imposed by the porous structure of tested materials. Adsorption of probe molecules is another attractive approach. Both types of approaches will be presented in this work. The methodology developed in this work on zeolites Beta, USY and silica-alumina may be appropriate for determination of accessible mesoporosity in other types of dealuminated zeolites as well as in hierarchical materials presenting combinations of various types of pores. 

Seeding technique. Al-free Ti-beta obtained by use of dealuminated zeolite-beta seeds Fluoride method. Al-free Ti-beta synthesis from a reaction mixture containing TEAOH and fluoride ions (HF) at near-neutral pH. Gel composition Ti02 60SiO2 32.9NEt4OH 32.9HF 20H2O 457.5 H20. Crystallization at 413 K with rotation of the autoclave (60 rpm)... 

SURFACE COMPOSITION AND DEPTH PROFILE OF DEALUMINATED ZEOLITES (43,44)... 

Infrared bands of dealuminated zeolites in the 0-H stretching region have been extensively studied (14-17) however, emphasis will be placed on the study by Fritz and Lunsford (10), which describes the effect of Na+ on these infrared bands. Perhaps the most informative example is the SiClA-treated zeolite (series A of Figure 3). The SiCl4-treated zeolites have less extraframework aluminum than do the steamed samples therefore, the infrared spectra in the 0-H stretching region are less complicated. 

The 27A1-MAS-NMR spectra of dealuminated zeolite Y generally consist of three signals indicative of three types of aluminum, but the intensity does not account for all the aluminum in the sample. The authors ascribe the difference to NMR-invisible Al previously determined (30) from an analysis of the 29Si-MAS-NMR data for dealuminated HY samples. The NMR resonance at 60 ppm for framework Al is relatively sharp. Octahedrally coordinated non-... 

Selectivities and activities of dealuminated zeolite Y are dependent on the method of dealumination and the "state" of the aluminum... 

The structural features of dealuminated zeolite samples were characterized using X-ray powder diffraction, porosimetry and solid-state NMR measurements. Hexadecane cracking was used as a probe reaction to investigate catalytic properties of pure zeolites. 

Figure 6. Cracking activity of dealuminated zeolites as a function of total aluminum content.

Characterisation and Catalytic Properties of Dealuminated Zeolite-Y A Comparison of Ammonium Hexafluorosilicate and Hydrothermal Treatments... 

The cracking activity and selectivity for n-heptane and gas-oil, of a series of dealuminated HY zeolites (SiCl4 or steam dealuminated) have been measured. The results have been related with the different types of aluminium and acid groups present and to the pore volume distribution. It is clearly shown that the unit cell parameter (framework Si/Al ratio) can not explain, by itself, the activity and selectivity of dealuminated zeolites. 

The synthesis of Sn-beta (68,151) with isolated single tin sites was accomphshed in a fluoride medium TEOS was hydrolyzed in a stirred aqueous solution of TEAOH. Then a solution of SnC 5H2O in water was added and the mixture stirred until the ethanol formed by hydrolysis of the TEOS had evaporated. HF was added to the resulting clear solution, and a thick paste formed. Then a suspension of nanocrystalline seeds (20 nm in diameter) of dealuminated zeolite beta in water was added. The crystallization was carried out in aTeflon-hned stainless-steel autoclave, which was heated to a temperature of 140 °C and continuously rotated for 20 days. After drying and calcining of the resultant sohd, XRD showed that a highly crystalline material with BEA structure was obtained, which contained 1.6 wt% Sn according to chemical analysis. Further characterization by XRD and UV, IR, and Sn MAS NMR spectroscopies verified the structure and the isomorphous substitution of siHcon by tin. 

In order to avoid any polymerization of ethylene on acid sites experiments were conducted at 210 K on a series of dealuminated zeolites. The figure 9 shows the increase in Av as the framework A1 content decreases. For this series of materials prepared by steaming followed by acid leaching, the acid strength increases up to an A1 atomic fraction close to 0.05 (29). 

The previous sections concern the activity and average density of active sites. It is of interest to know whether variation in the distribution of rduminiiun sites in zeolites having the same framework composition (Si/Al) can be achieved. This possibility is suggested by the earlier discussion concerning dealumination and there are also suggestions that re-alumination of dealuminated zeolites can result in differences in aliuninium distribution from that in parent synthetic materials having the same overall composition. 

A series of dealuminated zeolites Y with framework n(Si)/n(Al) ratios of 2.8-6.0 was prepared by steaming and characterised by atomic emission spectroscopy and A1, and Si NMR spectroscopy. ... 

Maache, M., Janin, A., LavaUey J.C., and Benazzi, E. FT-infrared study of Br0nsted acidity of H-mordenites heterogeneity and effect of dealumination. Zeolites 1995,15,507-516. 

Aramburo LR, Karwacki L, Cubillas P, Asahina S, de Winter DAM, Drury MR, et al. The porosity, acidity, and reactivity of dealuminated zeolite ZSM-5 at the single particle level the influence of the zeolite architecture. Chemistry 2011 17 13773-81. 

Influence of structure on the number and strength of available Brdnsted acid sites was investigated on a series of dealuminated zeolites (HY, mordenite, ZSM-5 and... 

The present review is aimed at covering first the literature which has appeared since about 1985 on both methodical and mechanistic aspects of dealumination techniques and on their structural and compositional consequences although fundamental and pioneering contributions published before this date will also be included. Progress made in the last decade in the field of alumination and desili-cation of zeolites, i.e., of processes closely related in nature to the main subject, will also be reviewed. However, this review does not refer to papers dealing exclusively or predominantly with special properties (e.g., acidity, catalytic activity, hydrophobicity) and applications of dealuminated zeolites and to the isomor-phous replacement of framework aluminum by elements other than silicon. 

We would like m sincerely acknowledge Mrs BURNICHON, DUPONT, LEVEQUE, RUS-SMANN and TC OSSI fw the preparation of dealuminated zeolites and adsoqition measurments. 

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