| Popis: |
The conversion of light paraffins into reactive olefins is becoming more important in view of the increasing requirements of environmental rules. The study of their diffusion and sorption behaviour in zeolites, typically employed as catalysts, might contribute to the understanding of their transformation. We have approach this study by computational means. The six C4 isomers, n- and iso-butane, and the n- (1-, cis- and trans-) iso-butene in two protonated zeolitic structures: ferrierite (H-Fer) and mordenite (H-Mor) were considered. It was used a simulation strategy which combines molecular mechanics (MM) and dynamics (MD), to provide information about the energetics of sorption and the diffusion properties of the organic molecules. The results, when qualitatively compared, could be extrapolated to explain the catalytic properties of the two solids on the paraffin and olefin molecules. In particular, they provide a rationale for the experimentally observed very high selectivity of H-Fer for the skeletal isomerization of n- butenes, as well as its rapid deactivation. These findings are of relevance in understanding the considerable activity of zeolites in the conversion of paraffins and olefins. Both, sorption and diffusion are controlling factors in the final selectivity of the zeolite catalyst. |
