Zeolites hydrocarbons, molecular mobility

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

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

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... 

Syngas conversion to methanol has been shown to take place on supported palladium catalyst [1]. Methanol can in turn be converted to gasoline over ZSM-5 via the MTG process developed by Mobil [2]. In recent work we have reported syngas (CO/H2) conversion to hydrocarbon products on bifunctional catalysts consisting of a methanol synthesis function, Pd, supported on ZSM-5 zeolites [3]. Work on syngas conversion to hydrocarbon products on Pd/SAPO molecular sieves has been published elsewhere [Thomson et. al., J. CataL. in press].Therefore, this paper will concentrate on propylene conversion. 

In contrast, for zeolite NaX the reduction of the molecular translational mobility with increasing sorbate concentration is mainly due to the reduction of the jump lengths, with jump rates practically unaffected by concentration. For hydrocarbons in NaX, the jump lengths are found to be corre-... 

Ab-initio density-functional molecular dynamics is used to characterize dynamical processes in zeolites. Simulations performed on the structure of gmelinite show that the proton transfer between the 0-sites is a spontaneous process enabled in both Na-free and Na-zeolite by just one water molecule adsorbed to the acid site. A proton attack of the acid zeolite at the hydrocarbon molecule is investigated at increased temperature of 700 K. In the protonated molecule a series of proton jumps are observed indicating their high mobility. 

Figure 13 displays the self-diffusivities of n-hexane and 2-methylpentane in silicalite-1 and H-ZSM-5 as a function of the ratio of the hydrocarbons. The self-diffusivities of both hexanes linearly decrease with increasing gas-phase fraction of the branched hexane in the gas phase for the non-acidic and acidic zeolite. In H-ZSM-5, the mobility of alkanes is approximately two times slower than in silicalite-1. Obviously, the presence of acid sites strongly affects the molecular transport due to stronger interactions with the n-hexane molecules. A similar effect of Bronsted sites on the single component diffusion of aromatics was observed in MFI zeolites with different concentration of acid sites [63-65]. The frequency response (FR) technique provided similar results... 

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