Coke location in microporous and hierarchical ZSM-5 and the impact on the MTH reaction

The deactivation and reactivation of microporous and hierarchical ZSM-5 zeolites have been studied in the methanol-to-hydrocarbon (MTH) reaction. The hierarchical ZSM-5 was synthesized via the desilication reassembly technique using cetyltrimethylammonium bromide as a surfactant. The catalysts differed significantly in the catalytic behavior after the reactivation procedure. This is ascribed to a different coke location in the deactivated catalysts arising from the difference in the porosity. The microporous ZSM-5 showed a coke gradient over the particle with a stronger accumulation of carbonaceous species in the outer particle layers, whereas a homogeneous coke distribution was observed for the deactivated hierarchical ZSM-5. Due to the diverging coke distribution, the irreversible damage of the zeolitic structure caused by reactivation differs for both catalysts. This fact is assumed to be the reason for the different deactivation/reactivation behaviors of these two zeolitic systems.