A series of ZSM-12 samples were prepared by calcining them at different temperatures that are
much higher than what is normally used. The catalytic activities of these samples were tested
using cracking of n-hexane at 400 °C. It was found that the cracking activities of samples calcined
at certain temperatures were unusually high: 3−4 times greater than that of the regular sample,
which was calcined at 550 °C. Interestingly, this enhanced activity was observed at two separate,
relatively narrow, ranges of temperatures: one around 650 °C and the other around 800 °C.
Brönsted and Lewis acid sites attributed to extraframework cationic aluminum were quantified
with Fourier transform infrared of adsorbed pyridine. The Lewis/Brönsted ratios of the enhanced-activity samples were high compared those of the low-activity samples; the trend in variation of
the Lewis/Brönsted ratios of the samples with calcination temperature closely mirrored the trend
observed for the catalytic activities. This is an indication that there is a synergistic interaction
between the Brönsted and Lewis acid sites that is responsible for the enhanced cracking activity.
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