Mapping the coke formation within a zeolite catalyst extrudate in space and time by operando computed X-ray diffraction tomography

We have used operando X-ray diffraction computed tomography (XRD-CT) analysed by rigorous crystallographic methods to reveal the behaviour of a zeolite/alumina based catalyst extrudate in the methanol-to-hydrocarbon reaction under working conditions (T-reaction = 440 degrees C; ambient total pressure; WHSV = 12 g(MeOH)g(extrudate)(-1)h(-1)). By doing so, we demonstrate that it is possible to precisely monitor how the cylindrical extrudate is deactivated during the process by gradual filling with coke from the outer surface towards the core. The operando data thus collected are simulated by a model taking both the reaction kinetics and the diffusion within the extrudate into account, and this analysis provides the tools required for future optimization of the degree of utilization of the catalyst. Both the operando experiment and post mortem XRD-CT of fully deactivated extrudates from a test reactor show clearly that the core of the catalyst body, around 1/3 of its volume, remains completely untouched by the reaction, even when the reactor output indicates zero activity. (C) 2021 The Author(s). Published by Elsevier Inc.

Automated summary

The study used operando X-ray diffraction computed tomography to investigate the deactivation process of a zeolite/alumina based catalyst extrudate in the methanol-to-hydrocarbon reaction. The results showed that the core of the catalyst body remained unaffected by the reaction, even when the reactor output indicated zero activity.