posted on 2015-12-17, 09:55authored byMichiel Dusselier, Mark A. Deimund, Joel E. Schmidt, Mark E. Davis
Zeolite SSZ-39 is evaluated for catalyzing
the methanol-to-olefins
(MTO) reaction. By steaming NH4–SSZ-39, Al can be
removed from framework positions, resulting in an increase in framework-Si/AlT and thus a lowered active acid site density. The Si/AlT ratios can be controlled by the steaming temperatures. SSZ-39
steamed at 750 °C, with preserved pore volume and morphology,
is an excellent MTO catalyst, as high, stable olefin selectivities,
long time-on-stream activity, and low alkane production are observed.
Moreover, interesting propylene/ethylene/butylene ratios of 2.8/1/1.1
are obtained, likely related to the shape of the AEI cage. By Cu2+-exchanging SSZ-39, evidence is provided to show that AlT sites in close proximity (high AlT density) produce
the unwanted effects (higher alkane-make and carbonaceous deposits)
in nonsteamed materials during MTO.