In situ synthesis of Ni-based catalyst for ambient-temperature CO2 methanation using rare-metal hydrides: Unveiling the reaction pathway and catalytic mechanism

Converting CO₂ into high value-added chemical fuels through coupling with renewable hydrogen, has emerged as a pivotal strategy to address environmental pollution and tackle energy supply issues. However, the high chemical inertness of CO₂ molecules and the complex multi-electron transfer processes involved in CO₂ hydrogenation pose significant challenges, leading to large energy barriers and poor product selectivity. Traditional chemical catalysts typically require harsh conditions such as high temperatures, pressures, and/or additives to overcome these barriers and accelerate sluggish reaction kinetics. Herein, we report a mechanochemical-force-driven strategy for the in situ synthesis of Ni nanoparticles supported on La₂O₃ (Ni/La₂O₃), which enables efficient CO₂ methanation at room temperature using LaNi₅ and H₂/CO₂ mixed gas as source materials. The experimental findings assuredly corroborate that CO₂ methanation proceeds through the formate route in the LaNi₅-[CO₂+H₂] system. This pathway involves the absorption of H₂ by LaNi₅, dissociation of hydrogen atoms, and their reaction with the formed La₂O₃ to generate surface hydroxyl groups. These hydroxyl groups play a crucial role in facilitating the dissociative adsorption of CO₂ on La₂O₃, resulting in the formation of carbonate and bicarbonate intermediates. Subsequently, these intermediates are continuously hydrogenated by the hydrogen atom flux from LaNi₅H_x, ultimately producing formate and methane. Our experimental and computational results demonstrate that modulating a metallic Ni active site center through direct interaction with a La₂O₃ support and exposing CO₂ to active hydrogen atoms sourced from metal hydrides may be a powerful strategy for promoting novel reactivity paradigms in CO₂ catalytic reduction reactions.