Reinforcing the Efficiency of Photothermal Catalytic CO2 Methanation through Integration of Ru Nanoparticles with Photothermal MnCo2O4 Nanosheets

Carbon dioxide (CO₂) hydrogenation to methane (CH₄) is regarded as a promising approach for CO₂ utilization, whereas achieving desirable conversion efficiency under mild conditions remains a significant challenge. Herein, we have identified ultrasmall Ru nanoparticles (∼2.5 nm) anchored on MnCo₂O₄ nanosheets as prospective photothermal catalysts for CO₂ methanation at ambient pressure with light irradiation. Our findings revealed that MnCo₂O₄ nanosheets exhibit dual functionality as photothermal substrates for localized temperature enhancement and photocatalysts for electron donation. As such, the optimized Ru/MnCo₂O₄-2 gave a high CH₄ production rate of 66.3 mmol g_cat^-1 h^-1 (corresponding to 5.1 mol g_Ru^-1 h^-1) with 96% CH₄ selectivity at 230 °C under ambient pressure and light irradiation (420-780 nm, 1.25 W cm^-2), outperforming most reported plasmonic metal-based catalysts. The mechanisms behind the intriguing photothermal catalytic performance improvement were substantiated through a comprehensive investigation involving experimental characterizations, numerical simulations and density functional theory (DFT) calculations, which unveiled the synergistic effects of enhanced charge separation efficiency, improved reaction kinetics, facilitated reactant adsorption/activation and accelerated intermediate conversion under light irradiation over Ru/MnCo₂O₄. A comparison study showed that, with identical external input energy during the reaction, Ru/MnCo₂O₄-2 had a much higher catalytic efficiency compared to Ru/TiO₂ and Ru/Al₂O₃. This study underscores the pivotal role played by photothermal supports and is believed to engender a heightened interest in plasmonic metal nanoparticles anchored on photothermal substrates for CO₂ methanation under mild conditions.