Multimodal Hard X-Ray Nanotomography Probes Pore Accessibility of Technical Catalysts after Coking

Coking is a common catalyst deactivation route in industrial processes involving carbonaceous species. While coking is easy to diagnose, this is often performed by bulk analysis. Understanding specific symptoms such as pore blockage and obstruction of active sites is especially challenging for technical catalysts and requires a spatially-resolved approach. Here a combination of ptychographic X-ray computed tomography (PXCT) and X-ray fluorescence nanotomography (XRF-CT) could identify and allocate regions of coke deposition within a technical zeolite-based propane dehydrogenation catalyst. PXCT is sensitive to the quantitative electron density of the sample, therefore indirectly visualising coke deposition in meso- and macropores with 56-61 nm 3D spatial resolution. For more direct visualisation the catalysts were treated with Cu solution as fluorescent marker, whereby complementary XRF-CT analysis could distinguish accessible and blocked pores based on the presence or absence of adsorbed Cu. This strategy was used to assess coking as a function of time on stream, to evaluate coke removal by oxidative regeneration, and to distinguish the presence of coke deposits separately within the zeolite and binder components. This strategy is applicable to virtually any porous solid catalyst and can deliver previously unknown insights into the common phenomenon of coke deposition particularly in technical catalysts. X-ray nanotomography visualises and distinguishes coke deposition sites within individual components of a technical catalyst composite. An accurate nanoscale view of catalyst deactivation and regeneration is achieved. image