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 behavioural characterisation of thousands of individual particles within the spatial confines of a hierarchically structured support but also a characterisation of their ensemble behaviour and local support interactions. Here, we introduce in-situ ptychographic X-ray computed nanotomography as a tool to facilitate this characterisation, 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 nanometres through the support. These observations expand the current understanding of sintering behaviour in supported catalysts and demonstrate PXCT’s capability to resolve restructuring processes within complex porous materials.