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کاتالیزور کاربردی a: عمومی 2012
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  • low temperature conversion of linear c4 olefins using acid zsm-5 zeolites with aluminum concentration gradient

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    • تاریخ ارائه: 1392/07/24
    • تاریخ انتشار در تی پی بین: 1392/07/24
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     two zsm-5 materials with high and low overall si/al ratio, each with an al concentration gradient across the crystals (g-samples) have been synthesized, physico-chemically characterized with several techniques (xrd, sem, n2 adsorption, 27al mas nmr, nh3-tpd, ft-ir and tof-sims), and catalytically tested in the low-temperature dimerization of n-butenes, paying attention to coke formation. their acidic properties were found consistent with their framework aluminum content, except for a lower than expected number of brønsted acid sites as measured by ftir of adsorbed pyridine. the dimerization – cracking – realkylation mechanism, previously observed for n-butenes dimerization over acid zsm-5 with homogeneous aluminum distribution, was confirmed over g-type catalysts. the influence of hard coke content, observed in the previous work, on product selectivity and distributions was also found for g-type catalysts. the siliceous g-type catalyst, with low amount of hard coke and micropores partly accessible to reactants, shows shape-selectivity properties consistent with dominating intra-crystalline catalysis. the aluminous g-type catalyst, with high amount of hard coke, and micropores completely filled with aromatic carbonaceous residue, shows thermodynamically equilibrated products selectivity and distributions in agreement with extra-crystalline catalysis.

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