Surface and Catalytic Properties of Molten In–Sn and In–Ni for Methane Dry Reforming and Pyrolysis

Molten metals have been recently shown as promising catalysts for the pyrolysis and dry reforming of methane. Herein, we examine the surface properties of molten In–Sn and In–Ni alloys and their influence on the catalytic performance. In–Sn shows higher CO₂ and CH₄ conversions than either pure In or pure Sn, whereas In–Ni has higher conversions for CO₂ than pure In. To understand the reason for this, we quantified the surface composition using surface tension measurements and ab initio molecular dynamics (AIMD) simulations. We find that In–Sn has similar surface compositions to its bulk, whereas In–Ni has heavily enriched In surfaces. Density functional theory calculations indicate that both Sn and Ni modify the electronic state of In, which is supported by XPS measurements. A qualitative correlation is identified between the surface charge on In and measured activity. Accumulation experiments showed minimal oxygen uptake at the steady state for both In–Sn and In–Ni systems. AIMD simulations are performed to understand the nature of intermediate oxygen and carbon species formed during the reaction and their effect on the surface composition of the alloy. The findings in this work highlight the crucial role of alloying elements in tuning catalyst surfaces, demonstrating the role of electronic effects, oxidation behavior, and intermediate accumulation.