Abstract Precise control over synergistic interactions is essential for the rational design of bimetallic catalysts, yet the governing role of metal particle size remains elusive. Here, we uncover a general size‐dependent principle that dictates structural and functional transitions in Ni‐Ru/CeO 2 catalysts during the co‐conversion of biomass and CO 2 . Atomically dispersed Ni and Ru sites on CeO 2 exhibit pronounced synergistic effects that markedly enhance CO 2 reforming of biomass, arising from the presence of independent metallic sites. In contrast, Ni nanoparticles with interspersed Ru form Ni‐Ru alloys that confer exceptional stability with only moderate activity loss. This size‐dependent structural transition induces a functional switch governing reaction pathway, coke deposition from encapsulated carbon to carbon nanotubes, and the trade‐off between catalytic activity and durability. These findings elucidate the mechanistic basis of size‐dependent interactions in Ni‐Ru bimetallic systems and guide the rational design of stable, high‐performance catalysts.
Shen et al. (2026) studied this question.