Plasmon-Enhanced CO₂ Methanation over Au@Ru/TiO₂ via Nanoscale Control of Ru Shell Thickness

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 TiO₂ to create hybrid catalysts for CO₂ methanation. By controlling Ru shell thickness, we identifyAu₆₀Ru₄₀/TiO₂, 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 TiO₂ induces strong metal-support interactions, upshifts the Ru d-band center, strengthens CO₂ adsorption, and lowers the barrier for the first hydrogenation step, shifting the rate-limiting step to CH₄ desorption. These results establish Au@Ru/TiO₂ as an efficient platform for visible-light-assisted thermocatalysis and demonstrates that nanoscale shell engineering as a generalizable strategy to optimize plasmonic catalysts for CO₂ hydrogenation and beyond.