APCATA 431– 2012-104

Interaction of Zn2+ with extraframework aluminum in HBEA zeolite and its role
in enhancing n-pentane isomerization

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(OAl )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.