B zeolite

Vinyl chloride is an important monomer for polyvinyl chloride (PVC). The main route for obtaining this monomer, however, is via ethylene (Chapter 7). A new approach to utilize ethane as an inexpensive chemical intermediate is to ammoxidize it to acetonitrile. The reaction takes place in presence of a cobalt-B-zeolite. 

Figure 2. Scanning electron microscopy of (a) zeolite X-chitosan, (b) zeolite Y-chitosan and (c) mordenite-chitosan composites prepared by encapsulation of zeolites during the gelling of chitosan.

A modification of the above cyclic method has proved more effective in the dealumination of Y zeolites. An almost aluminum-free, Y-type structure was obtained by using a process involving the following steps a) calcination, under steam, of a low-soda (about 3 wt.% Na O), ammonium exchanged Y zeolite b) further ammonium exchange of the calcined zeolite c) high-temperature calcination of the zeolite, under steam d) acid treatment of the zeolite. Steps a) and c) lead to the formation of ultrastable zeolites USY-A and USY-B, respectively. Acid treatment of the USY-B zeolite can yield a series of aluminum-deficient Y zeolites with different degrees of dealumination, whose composition depends upon the conditions of the acid treatment. Under severe reaction conditions (5N HC1, 90°C) an almost aluminum-free Y-type structure can be obtained ("silica-faujasite") (28,29). 

Using Si-NMR spectra to calculate the SiO /Al O ratio in the framework and chemical analysis to determine the overall SiO /Al O ratio, Lippmaa et al. (38) concluded that in their sample of USY-A zeolite, 33 Al/u.c. are in the framework and 24 Al/u.c. are in non-framework positions (42 percent framework dealumination). In the USY-B zeolite prepared from the same parent NaY, Lippmaa et al. found 4 Al/u.c. in the framework and 53 Al/u.c. in non-framework positions (93% framework dealumination). 

The unusually high stability of DAY zeolites prepared from USY-B and having SiO /Al O ratios over 100 indicates that the non-framework aluminum species present in USY-B play no role in enhancing the stability of this zeolite. It is the highly silicious framework, in which most of the aluminum has been replaced by silicon atoms, that is responsible for the high stability of USY-B zeolites and of corresponding DAY zeolites. In zeolites with a lesser degree of framework dealumination (i.e. in USY-A), the non-framework aluminum species appear to play a role in the stabilization of the zeolites, since their removal results in materials of lesser stability (28). 

The adsorption capacity of DAY is greater than that of USY-B zeolites, due to the removal of A1 species from the zeolite pores. 

Using the n-buthylamine titration method, Scherzer and Humphries (18) have shown that USY-B zeolites have considerably less acidity than USY-A zeolites. This is due to the more advanced thermal dealumination of USY-B, which reduces both Bronsted and Lewis type acidity. 

Fig. 13. The nuclear magnetic spin-lattice relaxation rate for water protons as a function of magnetic field strength reported as the proton Larmor frequency at 298 K for 5% suspensions of the particulate stabilized in a 0.5% agar gel presented as the difference plot (A) Zeolite 3A (B) Zeolite 13X (C) Zeolite NaY (D) kaolin with 7 s added to each point to offset the data presentation (E) Cancrinite with 9 s added to each point to offset the data presentation and (F) 0.5% agar gel profile with 10 s added to each point. The solid lines are fits to a power law (68).

Figure 2. Temperature Programmed Reduction of Ni contaminated catalyst components a) non-zeolitic particles with 10,100 ppm Ni b) zeolitic particles with 10,860 ppm Ni. These materials were impregnated using nickel naphthenate and then steamed (1450°F, 4 hrs, 90% steam, 10% air) prior to running the TPR. The Ni on the non-zeolitic particles reduced at a lower temperature than that on the zeolitic particles.

FIGURE 7.6 Zeolite frameworks built up from sodalite units (a) sodalite (SOD), (b) zeolite A (LTA), and (c) faujasite (zeolite X and zeolite Y)... 

B. Zeolites for which the individual spectral signals are composites and cannot be assigned to Si(nAI) structural units... 

Fig. 40. High-resolution 29Si MAS NMR study of progressive ultrastahilization of zeolite Y (Si/Al = 2.37) (165). Upper spectra without, lower spectra with cross-polarization, (a) and (b). Zeolite Na-Y (sample 1) (c) and (d), sample 1 after 50% NH exchange (sample 2) (e) and (0, sample 2 after DB treatment at 540°C for 3 hr (sample 3) (g) and (h), sample 3 after extraction with 0.1 M HC1 for 3.5 hr at 100°C (sample 4) (i) and (k), sample 3 after twofold ammonium exchange and DB treatment at 815°C for 3 hr (sample 5) (1) and (m), sample 5 after extraction with 0.1 M HC1 for 3.5 hr at 100°C (sample 6).

Fig. 31. Distribution functions of the jump time (NMR) at 0 °C for liquid water, ice, adsorbed water on a) porous glass AG 39, b) zeolite, c) charcoal and d) bacterial cell walls. (Belfort etal.196))...

Figure 1. Representative zeolite structures where the open framework is represented by sticks joining the Si or A1 atoms. Oxygen bridge atoms lie roughly at the mid-point of these atoms and are omitted for clarity, a) zeolite Y b) zeolite A...

Figure 5.7 Zeolite structure, (a) 6-ring containing two aluminium and four silicon tetrahedral centres, (b) Zeolite A structure. Each of the eight sodalite units depicted contains 24 aluminium or silicon tetrahedral centres arranged to give six 4-rings plus eight 6-rings...

Figure 3.9 Schematic of the process used by Pinnavaia et al. for the preparation of steam-stable aluminosilicate nanostructures assembled from zeolite seeds, (a) Nanosize zeolites (zeolite seeds) (b) zeolite seeds assembling around the surfactant (CTAB) (c) assembled structure and,...

Figure 7.7. Schematic representation showing framework structures of (a) zeolite A, (b) zeolites X and Y, (c) erionite and (d) chabazite.

Derouane, E. G., Dillon, C. J., Bethell, D., Derouane Abd-Hamid, S. B. Zeolite catalysts as solid solvents in fine chemicals synthesis-1. Catalyst deactivation in the Friedel-Crafts acetylation of anisole, J. Catal., 1999, 187, 209-218. 

Claridge, R. P., Llewellyn, Lancaster, N. Millar, R. W., Moodie, R. B. and Sandall, J. P. B. Zeolite catalysis of aromatic nitrations with dinitrogen pentoxide, J. Chem. Soc., Perkin Trans. 2, 1999, 1815-1818. 

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