• interaction of zn2+ with extraframework aluminum in hbea zeolite and its role in enhancing n-pentane isomerization

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    • تاریخ ارائه: 1392/07/24
    • تاریخ انتشار در تی پی بین: 1392/07/24
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     the electrodeposition method was used to produce zn2+ cation precursors, followed by the introduction of zn2+ cation precursors to hbea by the ion exchange technique. the introduction of zn2+ cations slightly changed the specific surface area and crystallinity of hbea. ir, xps and solid state mas nmr results showed that zn2+ cations interacted with (alo)+ extraframework aluminum to form zn(oaldouble bond; length as m-dash)2 and simultaneously induced the formation of bridging hydroxyl groups, si(oh)al. the pyridine adsorbed ir study revealed that the presence of zn2+ cations fully eliminated weak and partially eliminated strong brønsted acid sites. as a result, strong and relatively weak lewis acid sites were formed in which the pyridine probe molecule desorbed at 623 k and below. the presence of zn2+ cations enhanced the catalytic activity of hbea in n-pentane isomerization due to the presence of strong lewis acid sites; the sites may facilitate the formation and maintenance of active protonic acid sites through a hydrogen spillover mechanism. at 598 k, the yield of isopentane for zn-hbea was 25.7% higher than that of hbea. within a reaction temperature range of 373–648 k, the apparent activation energy for isomerization of n-pentane over hbea and zn-hbea was 118.76 and 90.79 kj/mol, respectively.

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