Plasmon‐Enhanced CO ₂ Methanation over Au@Ru/TiO ₂ via Nanoscale Control of Ru Shell Thickness

Abstract Plasmonic‐catalytic nanostructures enable coupling light harvesting with chemical transformations, yet their performance critically depends on nanoscale architecture and metal‐support interactions. Here, we synthesize Au@Ru core–shell nanoparticles with tunable Ru coverage and immobilize them on TiO 2 to create hybrid catalysts for CO 2 methanation. By controlling Ru shell thickness, we identifyAu 60 Ru 40 /TiO 2 , featuring a thin, discontinuous shell (∼2 nm Ru nanocrystallites), as the most active composition. This catalyst combines abundant Ru active sites with preservation of the Au core's localized surface plasmon resonance (LSPR). Under 545 nm illumination, it shows a 335% rate enhancement over dark conditions at 190 °C, outperforming commercial Ru/C and remaining stable for 85 h. Optical, structural, and kinetic analysis indicate that illumination accelerates the methanation without changing the rate‐determining step, consistent with a dominant photothermal contribution. Density functional theory reveals that TiO 2 induces strong metal‐support interactions, upshifts the Ru d‐band center, strengthens CO 2 adsorption, and lowers the barrier for the first hydrogenation step, shifting the rate‐limiting step to CH 4 desorption. These results establish Au@Ru/TiO 2 as an efficient platform for visible‐light‐assisted thermocatalysis and demonstrates that nanoscale shell engineering as a generalizable strategy to optimize plasmonic catalysts for CO 2 hydrogenation and beyond.