In heterogeneous catalysis, spatiotemporal variations in catalyst oxidation state and performance can arise from gradients in reactant concentrations, pressure, and temperature.[1] In dry methane reforming (DMR), thermodynamic calculations predict that nickel does not oxidize under any conditions, and hence no gradients are expected.[2] However, monitoring oxidation state variations over the reactor bed is challenging with conventional analytical or spectroscopic techniques.

Using Full-Field X-ray Micro-imaging (FF-TXM), we were able to monitor heterogeneities in the oxidation state of Ni during DMR and regeneration, with 11 s time resolution and 1.625-micrometer spatial resolution.[3] As expected from previous literature, no significant gradients in the oxidation state were observed over the length of the catalyst bed during DMR, although small variations in temperature in the bed can lead to localized differences in oxidation state. Furthermore, we observed distinct oxidation and reduction dynamics when changing reaction conditions, depending on catalyst composition. Our findings highlight the importance of performing spatiotemporal spectroscopy measurements. The relevance of these findings for DMR catalyst design will be discussed.

1. Pinto, D., van der Bom Estadella, V., Urakawa, A., Sci. Technol., 17, 5349-5359 (2022).
2. Giehr, A., Maier, L., Schunk, S. A., and Deutschmann, O., ChemCatChem, 10, 751-757 (2018).
3. Briois, V., Nelayah, J., La Fontaine, et al., ChemCatChem 16, e202400352 (2024).

Sofie Ferwerda started her PhD at the Inorganic Chemistry and Catalysis group at Utrecht University in 2021. Her research is focused on using operando spectroscopy tools to study carbon formation and deactivation mechanisms during dry methane reforming. Her project is a part of the Advanced Research Center for Chemical Building Blocks consortium (ARC-CBBC) and is conducted in collaboration with BASF.