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 CHx 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.