Pyridine silicalite

Role of the organic feed XRD powder patterns and FT-IR spectra confirmed that pure MFI-type Ti-silicalite (TS-1) was obtained [18-23], with a surface area of 530 m g". FT-IR spectra of adsorbed pyridine (Fig. 39.2) showed the presence only of weak Bronsted and Lewis sites [24,25], as confirmed by the complete evacuation from the surface at 373 K. 

Recently, by using neutron powder-diffraction, it has been possible to localize the perdeuterated benzene (19) and pyridine (20) guests in high symmetry zeolites. In the case of MFI type frameworks (silicalite, ZSM-5, boralites, etc) the problem is somewhat different, since extensive peak-overlap occurs throughout the pattern (vide infra). In that case, most of the refinable parameters are highly correlated. These parameters form two distinct groups one corresponds to the profile parameters, which must first be varied the second corresponds to all the structural atomic parameters (x, y, z, thermal factors, occupancy). Some of which must be severely constrained. 

The interaction of different nitriles (acetonitrile, pivalonitrile and benzonitrile), of branched aliphatic compounds (2,2-dimethylbutane, reri-butyl-alcohol, methyl-rert-butylether, methyl and dimethylcyclohexanes) and of aromatics (benzene, toluene, ortho-, meta- and para-xylene, pyridine, picolines and lutidine) has been studied over four different ZSM5 zeolites, over silicalite-1 and titanium silicalite-1 and over boralite BOR-C. Internal, external and extraframework sites have been characterized and the access to the cavities discussed. 

Abstract Infrared spectroscopic methodsfor the measurement of adsorption and adsorption kinetics of some aromatics (benzene, ethylbenzene, p-xylene), pyridine, and paraffins in solid microporous materials such as zeolites (MOR, ZSM-5, silicalite-1) are described as well as the evaluation of the spectroscopically obtained data. The adsorption isotherms are of the Langmuir-Freundlich type. Isosteric heats of adsorption, transport diffusivities, and activation energies of diffusion as deduced from the spectroscopic measurements are compared with literature data as far as available, and they are found to be in reasonable agreement with results provided by independent techniques. Special attention is paid to sorption and sorption kinetics of binary mixtures, especially the problems of co- and counter-diffusion. ... 

The assumption that the strong interaction between the strongly acidic adsorbent and the strongly basic adsorbate under our experimental conditions was the reason for the failure to achieve reversibility was confirmed when adsorbents with the same structure but lower (Li-ZSM-5 or Na-ZSM-5) or zero acidity (silicalite-1) were employed [26]. Figure 12 demonstrates the perfect reversibility of pyridine sorption into the slightly acidic Li-ZSM-5 zeolite. 

Also, pyridine was reversibly adsorbed into the essentially nonacidic silicalite-1 (sample No. 4), which has the same MFI structure as H-ZSM-5, but no acid centers. A set of spectra of pyridine uptake into silicalite-1 was scanned in short intervals and is displayed in Fig. 13. 

Fig. 13 Set of FTIR spectra of successive states of uptake of pyridine into silicalite-1 (sample No. 4)...

When the strong acidity of the MFI zeolite (H-ZSM-5) was removed via ion exchange, as in the case of Li-ZSM-5 or Na-ZSM-5, or was intrinsically absent, as in the case of silicalite-1, adsorption of pyridine was entirely reversible, and reasonable ( corrected ) diffusion coefficients were obtained. As an example. Fig. 12 illustrates the reversible pyridine adsorption into and desorption out of Li-ZSM-5. The diffusion coefficient of pyridine transport in... 

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