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We investigated the formation of coke on zeolitic catalysts in the disproportionation of n -propylbenzene by means of 129 Xe, 27 Al, and 13 C NMR spectroscopy. According to 13 C CP-MAS (proton cross polarization with magic angle spinning) spectra, the coke formed in USY and ZSM-5 zeolites was classified into aliphatics and aromatics. It was found that aliphatic coke could be removed by a simple evacuation procedure. The location of the coke determined from 129 Xe NMR spectra and xenon adsorption isotherms varied with the zeolite catalysts. For zeolite USY, the coke was formed inside the supercages and is mainly polyaromatic. For zeolite ZSM-5. the coke is alkykaromatic and tended to deposit at the openings of the channels rather than at their intersections. In regard to the mechanism, the reaction on USY followed bimolecular kinetics, whereas on ZSM-5 the reaction was monomolecular.

The adsorption of benzene on dehydrated NaX (Si/Al=1.23) and NaY (Si/Al=2.49, 2.70) zeolites has been studied directly by 1 H and 13 C NMR measurements of the adsorbed benzene and probed indirectly by the combination of 129 Xe NMR and isotherm measurements of the coadsorbed xenon. Powders zeolite samples with varied adsorbate concentrations were investigated. Detailed macroscopic and microscopic adsorption phenomena of benzenc on faujasite-type zeolites, including the loading capacity, mobility, and sites of adsorption, are presented in terms of measurements of NMR line widths and chemical shifts

The adsorption behavior of benzene on dehydrated NaY zeolite has been studied by means of 129Xe n.m.r. and isotherm measurements of adsorbed xenon followed by proton and 13C n.m.r. of adsorbed benzene. Samples with varied benzene loadings were investigated. We found that to obtain a homogeneous molecular distribution in the zeolite cavities, thermal pretreatment of the sample at temperatures above 250°C for a period of several hours was necessary. The maximum number of benzene molecules that can be loaded within a zeolite supercage is found to lie between 4.9 and 5.2. 129Xe n.m.r. has provided valuable information about the arrangement and mobility of adsorbed benzene. To confirm the effect of heat treatment on benzene distribution within NaY supercages, we also examined the proton and 13C n.m.r. spectra of adsorbed benzene and compared them with published results.

The sorption and transport properties of benzene on dehydrated NaX and NaY zeolites have been investigated directly by 1H and 13C NMR measurements of the adsorbed benzene and probed indirectly by 129Xe NMR of the coadsorbed xenon. Dehydrated NaX and NaY zeolite adsorbate samples containing various adsorbate concentrations and having various sample bed configurations, which were subjected to different preparatory and experimental conditions, have been examined. Thermal treatment at a temperature (>250 °C) much greater than the boiling point of bulk benzene (80 °C) for an extended period of several hours is indispensable to ensure a homogeneous benzene distribution within the supercages of the faujasite-type zeolites.

The thermal stability of zeolite beta has been studied by 129Xe NMR and adsorption isotherm of adsorbed xenon in correlation with data from X-ray diffraction and 27Al magic-angle-spinning NMR experiments. Samples subject to different calcination and dehydration conditions were examined. Minor destruction of the crystalline framework resulting from dealumination processes has been found for samples treated at a temperature as small as 400°C. At higher temperatures, a severe process of dealumination involving the breaking of 12-membered rings leads to the conclusion that the maximum regeneration temperature of zeofite beta lies near 760°C.