Enhancing CO₂ Methanation via Plasma-Generated Atomic Hydrogen

Plasma catalysis has recently garnered significant attention due to its potential to induce synergistic effects through the interaction between plasma-generated species and catalyst surfaces. In hydrogenation reactions such as ammonia synthesis and CO₂ hydrogenation, plasma catalysis has demonstrated enhanced performance compared to conventional thermal catalysis. However, the mechanistic understanding of gaseous plasma-activated species, particularly their role on catalyst surfaces, remains limited. In this study, we investigated plasma-enhanced CO₂ methanation over Ni/Al₂O₃ and identified a distinct reaction pathway involving plasma-generated atomic hydrogen, which facilitates CO₂ methanation via an Eley–Rideal mechanism. Kinetic analysis, in situ plasma–surface characterization, and DFT calculations revealed that atomic hydrogen generated under plasma conditions promotes CH₄ formation by directly reacting with adsorbed species. Unlike the Langmuir–Hinshelwood mechanism dominant under thermal conditions, the presence of high-energy, translationally mobile atomic hydrogen introduces an Eley–Rideal reaction channel, effectively lowering the energy barrier for the rate-determining step. These findings provide mechanistic insight into the unique role of plasma-derived atomic hydrogen in enabling low-temperature CO₂ hydrogenation pathways beyond thermal limitations.