Ru-$\mathrm{Ce}{\mathrm{O}}_2$ catalysts, which combine the high catalytic activity of ruthenium with the unique redox properties of ceria, have demonstrated significant potential in various catalytic reactions including $\mathrm{C}{\mathrm{O}}_2$ methanation, ammonia synthesis, and oxidation-reduction processes. However, the physical mechanisms underlying their high performance remain incompletely understood primarily because there is limited knowledge regarding the structural evolution of Ru-$\mathrm{Ce}{\mathrm{O}}_2$ catalysts under near-realistic conditions. In this work we propose a strategy to investigate this structural evolution by integrating a global search algorithm based on first-principles computational data with electronic structure calculations to study the behavior of Ru-$\mathrm{Ce}{\mathrm{O}}_2$ under different redox conditions. Our results reveal that oxidizing conditions promote the dispersion of Ru clusters into atomic forms. These dispersed clusters are stabilized by the formation of bonds between Ru and lattice oxygen on the $\mathrm{Ce}{\mathrm{O}}_2$ surface. In contrast, reducing conditions enhance oxygen vacancy formation, which leads to the aggregation and sintering of atomic Ru species into larger metallic structures. Furthermore, charge transfer between Ru clusters and $\mathrm{Ce}{\mathrm{O}}_2$ plays a critical role. Oxidizing conditions facilitate electron transfer from Ru to $\mathrm{Ce}{\mathrm{O}}_2$, thereby stabilizing dispersed configurations while reducing conditions diminishing this interaction and promoting aggregation. These findings underscore the tunability of Ru cluster morphology through redox control and provide valuable insights into optimizing Ru-$\mathrm{Ce}{\mathrm{O}}_2$ catalysts for enhanced performance.

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• Electronic structure
• Structural properties
• Surfaces
• Density functional calculations