Lifecycle of Pd Clusters: Following the Formation and Evolution of Active Pd Clusters on Ceria During CO Oxidation by In Situ/Operando Characterization Techniques
Daria Gashnikova, Florian Maurer, Miriam R. Bauer, Sarah Bernart, Jelena Jelic, Mads Lützen, Carina B. Maliakkal, Paolo Dolcet, Felix Studt, Christian Kübel, Christian D. Damsgaard, Maria Casapu, Jan-Dierk Grunwaldt
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引用次数: 0
Abstract
For maximizing the atomic efficiency in noble metal-based catalysts, dedicated preparation routes and high lifetime are essential. Both aspects require an in-depth understanding of the fate of noble metal atoms under reaction conditions. For this purpose, we used a combination of complementary in situ/operando characterization techniques to follow the lifecycle of the Pd sites in a 0.5% Pd/5% CeO2–Al2O3 catalyst during oxygen-rich CO oxidation. Time-resolved X-ray absorption spectroscopy showed that Pd cluster formation under reaction conditions is important for a high CO oxidation activity. In combination with density functional theory calculations, we concluded that the ideal Pd cluster size amounts to about 10–30 Pd atoms. The cluster formation and stability were affected by the applied temperature and reaction conditions. Already short pulses of 1000 ppm CO in the lean reaction feed were found to trigger sintering of Pd at temperatures below 200 °C, while at higher temperatures oxidation processes prevailed. Environmental transmission electron microscopy unraveled redispersion at higher temperatures (400–500 °C) in oxygen atmosphere, leading to the formation of single sites and thus the loss of activity. However, due to the reductive nature of CO, clusters formed again upon cooling in reaction atmosphere, thus closing the catalytic cycle. Exploiting the gained knowledge on the lifecycle of Pd clusters, we systematically investigated the effect of catalyst composition on the cluster formation tendency. As uncovered by DRIFTS measurements, the Pd to CeO2 ratio seems to be a key descriptor for Pd agglomeration under reaction conditions. While for higher Pd loadings, the probability of cluster formation increased, a higher CeO2 content leads to the formation of oxidized dispersed Pd species. According to our results, a Pd:CeO2 weight ratio of 1:10 for CeO2–Al2O3-supported catalysts leads to the highest CO oxidation activity under lean conditions independent of the applied synthesis method.
期刊介绍:
ACS Catalysis is an esteemed journal that publishes original research in the fields of heterogeneous catalysis, molecular catalysis, and biocatalysis. It offers broad coverage across diverse areas such as life sciences, organometallics and synthesis, photochemistry and electrochemistry, drug discovery and synthesis, materials science, environmental protection, polymer discovery and synthesis, and energy and fuels.
The scope of the journal is to showcase innovative work in various aspects of catalysis. This includes new reactions and novel synthetic approaches utilizing known catalysts, the discovery or modification of new catalysts, elucidation of catalytic mechanisms through cutting-edge investigations, practical enhancements of existing processes, as well as conceptual advances in the field. Contributions to ACS Catalysis can encompass both experimental and theoretical research focused on catalytic molecules, macromolecules, and materials that exhibit catalytic turnover.