Molecular mobility measurement zeolite

Molecular mobility measurement, hydrocarbons in zeolites, 39 351-410 benzene... 

Molecular Mobility Measurement of Hydrocarbons in Zeolites by NMR Techniques... 

X type zeolites provide favourable conditions for nmr self-diffusion measurements, since in comparison with most other zeolite types, the open pore structure leads to higher molecular mobilities, as well as to larger (transverse) nuclear magnetic relaxation times, which -in turn - allow the application of larger observation times a. 

The nuclear magnetic resonance relaxation times for the protons of water adsorbed to saturation in a high-purity specimen of zeolite 13-X have been measured between 200° and 500°K. The data can be accounted for by the model of an intracrystalline fluid which is about 30 times as viscous as bulk water at room temperature, shows a broad distribution of molecular mobilities, and is about as dense as liquid water. The median correlation time (time between molecular flights) is... 

The diffusion properties of zeoUtes may be significantly influenced by their content of exchangeable cations. As an example, by both nuclear magnetic relaxation [1,143] and PEG NMR [145] measurements, the molecular mobility of aromatics in zeolite Na-X was found to be larger than in Na-Y. Since the adsorbate-adsorbent interaction of unsaturated hydrocarbons is dominated by the interaction between the n electrons of the double bonds and... 

The acidic properties of hydroxyl sites of H-Y zeolite were also measured at 473 K by adsorption calorimetry of various bases (piperidine, pyridine, and ammonia) by Tsutsumi et al. [109]. The difference in heats of adsorption between the OH sites was explained by a positional difference between the OH sites, molecular size of the titrating bases, and proton mobility induced by strong bases. The order of strength of bases was determined by replacing a base molecule by another one (for adsorption on H-Y zeolite) as follows piperidine (Qinit 165 kJ mol ) > pyridine (Qinit 160 kJ mol ) > ammonia (Qinit 125 kJ moh ). This order differs from the order expected from their pKa values in solution. Heats of adsorption were measured over a wide range of coverage in the case of ammonia, but only below ca. 3mmolg in the... 

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