(544bx) Stability of Fe and Zn Promoted Mo/ZSM-5 Catalysts for Ethane Dehydroaromatization in Cyclic Operation Mode

The stability of Fe and Zn promoted
Mo/ZSM-5 catalysts in ethane dehydroaromatization was studied. The catalytic
performance test was conducted in cyclic regeneration mode to elucidate the
deactivation and regeneration mechanism. The addition of Zn to Mo/ZSM-5
resulted in an initial increase in aromatic selectivity, however, the loss of
about 50% of the Zn resulted in a total decrease in aromatic selectivity over
the five regeneration cycles. The addition of Fe to Mo/ZSM-5 resulted in no
decrease in aromatic selectivity or aromatic yield throughout 5 regeneration
cycles.  The formation of carbon
nanotubes was discovered on Fe promoted Mo/ZSM-5 catalyst which was believed to
improve gas diffusion to micro pores. It was discovered that Fe and Mo
agglomerated particles remained on the catalyst surface at low Fe/Mo atomic
ratios resulting in the formation of base-grown carbon nanotubes.  When the Fe/Mo atomic ratio was high the
agglomerated particles were able to leave the surface of the zeolite resulting
in tip growth carbon nanotubes.  The temperature-programmed-reduction
profile of the Fe promoted Mo/ZSM-5 catalyst also suggested the formation of a
more stable Mo and/or Fe species at 615^oC.  The addition of Fe & Zn to Mo/ZSM-5
resulted in the loss of less Mo metal than the Zn promoted Mo/ZSM-5 catalyst.
This would suggest that Fe is a better stabilizer for the Mo/ZSM-5 than Zn.

Figure
1:  Time-on-stream benzene formation. Stability
is improved by adding Fe to the Mo/ZSM-5 over five reaction and regeneration cycles.