Alloying Co with Pt balances CO2 and methane activation in dry reforming of methane

Dry reforming of methane (DRM) converts the greenhouse gases CH₄ and CO₂ into synthesis gas (a mixture of H₂ and CO). Bimetallic catalysts offer tunable electronic and geometric properties that can overcome the stability and performance limitations of monometallic systems. Here, we investigate the structure and DRM activity of SiO₂-supported bimetallic CoPt nanoparticles (CoPt/SiO₂) and contrast them to their monometallic counterparts Co/SiO₂ and Pt/SiO₂. CoPt/SiO₂ exhibits significantly higher activity and stability under DRM conditions than the monometallic catalysts. Operando X-ray absorption and diffraction (XAS-XRD) measurements reveal that CoPt/SiO₂ forms an ordered intermetallic CoPt phase after pretreatment in H₂/N₂, which transitions to a disordered random alloy under DRM conditions at 800 °C, highlighting the dynamic behavior of the catalyst under reaction conditions. Further, operando Co K-edge XAS shows that Co/SiO₂ deactivates due to cobalt oxidation, whereas its alloying with Pt stabilizes Co in its metallic state. Density functional theory (DFT) calculations rationalize both the enhanced catalytic performance and the observed structural dynamics. On CoPt(111), CO₂ activation barriers are lower, and CH_x fragments bind more weakly than on Pt(111), alleviating the limitations of poor CO₂ activation and coke formation on monometallic Pt. Compared to Co(111), CoPt binds CO* and O* less strongly, reducing the propensity for surface oxidation. Surface free-energy calculations further reveal a strong adsorbate-dependent driving force for surface segregation and phase stability: H* stabilizes ordered CoPt surfaces, whereas O* strongly promotes Co surface segregation, favoring a transition to a disordered alloy. Together, these findings establish adsorbate-driven surface thermodynamics as a key mechanism driving the order–disorder transitions of CoPt under DRM conditions.