Zeolite faujasite basicity

Faujasite zeolites with a three dimensional strueture and 12-A supercavities are the most studied supports. Davis et al. [67,68] prepared eatalysts by impregnation of CsNaX and CsNaY with eesium acetate then thermal decomposition. They studied for first time the effect of loading cesium into zeolite on the acid-base properties, by studying the decomposition of propanol. Since then, special emphasis has been devoted to the study of cesium oxide loaded into faujasite zeolites yielding basicities in the range of superbasicity [66-69,73-76]. 

Since the initial work of Lippmaa et al. [18], there have been many studies of the Si MAS NMR spectra of low Si/Al ratio zeolites. The general features of these spectra are now well understood, and results from the early studies have been reviewed [1]. In general, the Si MAS NMR spectra of simple zeolites contain a maximum of five reasonably well-resolved peaks, as illustrated in Fig. 5 for the zeolite analcite. It was demonstrated by Lippmaa et al. [18] that these five peaks correspond to the five possible distributions of Si and Al around a silicon nucleus at the center of an Si04 tetrahedron namely, Si[4Al], Si[3Al, lSi], Si[2Al, 2Si], Si[Al, 3Si], and Si[4Si]. In addition, as shown in Fig. 6, the ranges of chemical shift over which the resonances occur are reasonably characteristic of the composition of the first coordination sphere, and the spectra may thus be used to probe the local Si/Al distributions in simple zeolite lattices. A particularly useful feature of these spectra is that the Si/Al ratio of the lattice can be calculated directly. This possibility has been investigated in detail for the previously described zeolite faujasite, which can be obtained by direct synthesis with the same basic structure but over a wide range of compositions (Si/Al = 1 -... 

Keywords basicity, faujasite, zeolite, MBOH, methylacetylene, H2S. 

The most commonly employed crystalline materials for liquid adsorptive separations are zeolite-based structured materials. Depending on the specific components and their structural framework, crystalline materials can be zeoUtes (silica, alumina), silicalite (silica) or AlPO-based molecular sieves (alumina, phosphoms oxide). Faujasites (X, Y) and other zeolites (A, ZSM-5, beta, mordenite, etc.) are the most popular materials. This is due to their narrow pore size distribution and the ability to tune or adjust their physicochemical properties, particularly their acidic-basic properties, by the ion exchange of cations, changing the Si02/Al203 ratio and varying the water content. These techniques are described and discussed in Chapter 2. By adjusting the properties almost an infinite number of zeolite materials and desorbent combinations can be studied. 

Heidler, R., janssens, G.O.A., Mortier, W.J., and Schoonheydt, R.A. (1995) Charge sensitivity analysis of intrinsic basicity of faujasite-type zeolites using the electronegativity equalization method... 

The adsorbent is an alkali exchanged faujasite bound into a bead. Because m-xylene is by far the most basic of the four mixed xylene isomers, the selectivity of the zeolite is tailored for this chemical trait. 

The protons released are presumably available to compensate for the loss of the charge balancing cations within the zeolite. In conventional syntheses, the phtha-lonitrile condensation normally requires the nucleophilic attack of a strong base on the phthalonitrile cyano group [176, 177]. This function is presumably accommodated by the Si-O-Al (cation) basic sites within the ion-exchanged faujasite zeolites [178, 179]. The importance of this role is perhaps emphasized by the widespread use of alkali metal exchanged faujasites, particularly the more basic NaX materials of higher aluminium content [180, 181] as hosts for encapsulated phthalocyanine complexes. 

Owing to the possibility of tuning (1) their acidic and basic properties, (2) their surface hydrophilicity, and (3) their adsorption and shape-selectivity properties, catalytic activity of zeolites was investigated in the production of HMF from carbohydrates. Whatever the hexose used as starting material, acidic pillared montmorillonites and faujasite were poorly selective towards HMF, yielding levu-linic and formic acids as the main products [81-83]. 

In X- and Y-type zeolites which exhibit the faujasite structure, the cations can reside in four basically different types of site which are located on the threefold axes of the cubic faujasite structure (Fig. 18). 

The results in Table 2 show that the pyridine is less active than any of the X zeolites and Ge faujasite except the lithium form which shows slightly lower activity, whereas all Y zeolites show lower activity than pyridine. Piperidine, however, is more active than any of the zeolite samples studied here. From this comparison, it appears that, most of the basic sites of the zeolites must have pK<10.3. However, the fact that zeolites are also active for catalyzing the condensation of benzaldehyde with ethyl malonate, indicate that these samples have some basic sites with pK< 13.3. On a quantitative bases, and comparing the activity of zeolites for condensation with ethyl cyanoacetate, ethyl acetoacetate and ethyl malonate (Fig. 2), we can conclude that most of the basic sites of the zeolite have pK<9.0 with a sensible amount with 9.0basic strength of different solid base catalysts. 

Huang, M., Adnot, A. and Kaliaguine, S. Characterization of basicity in alkaline cation faujasite zeolites - An XPS study using pyrrole as aprobe molecule, J. Catal., 1992,137, 322-332. 

In view of what precedes, it has been the aim of the present work to identify the Ru-species present in faujasite-type zeolites activated under WGS-conditions, making use of the avail-albe literature data. The activation procedure of Ru(III)hex-ammine in NaY has been related to its catalytic performance as low temperature WGS-catalvst. Subsequently, the basicity of the material was related to its catalytic behavior in the same reaction, by changing the nature of the parent complex, of the charge compensating cations and of the aluminum content of the faujasite-type zeolite. 

Oare earth forms of zeolites X and Y type faujasites possess superior catalytic properties for various reactions such as alkylation, isomerization, and cracking (9, 12, 18). Structural studies involving x-ray diffraction and CO chemisorption have been made to locate the positions of the rare earth (11, 14, 16). Hydroxyl groups and their relationship to surface acidity have been studied by infrared spectroscopy, utilizing the adsorption of pyridine and other basic molecules (2, 6, 21, 22, 23). Since much of the previous research has involved measurements on mixed rare earth faujasites, a need existed for a more systematic study of the individual rare earth zeolites, in regard to both structural and catalytic properties. The present investigation deals with the Y, La, Ce, Pr, Sm,... 

The protonic form of zeolite ZSM-5 Alj. Si,54 O,, Si/Al=35) obtained from MOBIL Corp. and a partially Rb ion exchanged form of X faujasite (Rb4 Naj4 Al Si,22 Oj, Si/Al=l. 75) obtained from Union Carbide Corp. were used as typical zeolites with an acidic and basic character, respectively. 

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