Enhanced Photo‐Thermal CO₂ Methanation with Tunable Ru_xNi_1‐x Catalytic Sites: Alloying Beyond Pure Ru

Abstract Developing solid‐solution nano‐alloys from immiscible metals has garnered significant interest; however, the high formation entropy poses substantial challenges in synthesis, hindering a comprehensive understanding of the catalytic mechanisms under alloying effects. Herein, the synthesis of small‐sized (≈2.5 nm) Ru_xNi_1‐x solid‐solution alloy nanoparticles with precisely controlled Ru/Ni ratios across a broad compositional range is reported for the first time, despite their bulk immiscibility. The Ru_0.76Ni_0.24/TiO₂ catalyst, with an optimized Ru/Ni ratio, delivers superior photo‐thermal catalytic activity for CO₂ methanation, achieving a CH₄ production rate of 3.58 mol g_metal⁻¹ h⁻¹ with 94% selectivity at 250 °C under light irradiation, representing a 2.82‐fold enhancement over monometallic Ru/TiO₂. Comprehensive investigations reveal that the reconstruction of electronic structure at Ru–Ni active sites enhances the adsorption/activation of reactants, promotes the transformation of intermediate HCO₃^* to HCOO^*, and facilitates the separation of the photo‐generated charge carriers witnessed by the femtosecond time‐resolved transient absorption (fs‐TA) spectroscopy. These combined effects collectively result in significantly enhanced CH₄ formation performance. This work highlights the potential of regulating catalytic sites in immiscible metal combinations for photo‐thermal catalytic CO₂ conversion, underscoring the promise of these cost‐effective alloys in heterogeneous catalysis.