Dynamic restructuring of Co-Pt nanoalloys during dry reforming of methane.

Abstract

The dry reforming of methane (DRM) converts two greenhouse gases, CH₄ and CO₂, into a synthesis gas, providing a route for CO₂ valorization. Bimetallic nanoparticles offer a versatile strategy to improve the performance of monometallic catalyst systems by altering the electronic and local structures of the active metal sites. Here, we investigate SiO₂-supported, Co _x Pt_1-x nanoalloys with varying composition (x = 0.1-0.9) for DRM. Structural characterization using pair distribution function analysis and electron microscopy revealed that the bimetallic nanoparticles feature fcc-type alloy structures with diameters of 1-2 nm, highly dispersed on SiO₂. Catalytic evaluation under DRM conditions shows that Pt-rich catalysts exhibit the highest initial CH₄ conversion rates, while increasing the Co content lowers the DRM activity and the H₂ : CO ratio due to an enhanced reverse water-gas shift activity. When normalized per Pt loading, the initial (20 min) CH₄ consumption rates remain largely unchanged, confirming Pt as the primary active site for CH₄ activation. Pt-rich catalysts deactivate rapidly with time on stream via coking (graphite), whereas alloying with Co improves their stability by suppressing carbon deposition. However, Co oxidation induces dealloying and contributes to deactivation, in particular at low temperatures (750 °C). Intermediate Co : Pt ratios, i.e., Co_0.5Pt_0.5-Co_0.7Pt_0.3, yield the best performing catalyst as they strike a balance between activity, H₂ : CO ratio, and stability, enabling an effective utilization of expensive Pt.