In situ ptychographic nanotomography captures activation, mobility, and deactivation of supported catalysts

Nanoparticles supported on the surface of porous carrier materials are the dominant form of heterogeneous catalysts today. Yet, they suffer from a common deactivation mechanism: the loss of active surface area under industrial use conditions. Deactivation often stems from the sintering of nanoparticles, a mass-transport process whose mechanism and operating length-scale are a topic of controversy. Investigating this process is challenging, requiring not only a behavioral characterization of thousands of individual particles within the spatial confines of a hierarchically structured support but also a characterization of their ensemble behavior and local support interactions. Here, we introduce in situ ptychographic X-ray computed nanotomography as a tool to facilitate this characterization, allowing a local examination of catalysts in their use-geometry under operational-relevant conditions. Applied to methane oxidation over a palladium-on-silica supported catalyst, we reveal two concurrently operating deactivation drivers, short-range ripening and long-range particle migration, each with different temperature and atmosphere dependencies. The latter enables particles to traverse hundreds of nanometers through the support. These observations expand the current understanding of sintering behavior in supported catalysts and demonstrate PXCT's capability to resolve restructuring processes within complex porous materials.