Plasma-Derived Atomic Hydrogen Enables Eley-Rideal-Type CO₂ Methanation at Low Temperatures

Activating H₂ molecules into atomic hydrogen and utilizing their intrinsic chemical reactivity are important processes in catalytic hydrogenation. Here, we have developed a plasma-catalyst combined system that directly provides atomic hydrogen from the gas phase to the catalytic reaction to utilize the high energy and translational freedom of atomic hydrogen. In this system, we show that the temperature of CO₂ methanation over Ni/Al₂O₃ can be dramatically lower compared to thermal catalysis. Using a detailed mechanistic study with kinetic studies, laser plasma diagnostics, in situ plasma surface characterization, and theoretical calculations, we revealed that plasma-derived atomic hydrogen (PDAH) plays a crucial role in reaction promotion. In particular, PDAH effectively lowers the energy barrier of bidentate formate hydrogenation by translating from the Langmuir-Hinshelwood to the Eley-Rideal-type reaction.