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

Abstract

Converting CO<inf>2</inf> 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 CO<inf>2</inf> molecules and the complex multi-electron transfer processes involved in CO<inf>2</inf> 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 La<inf>2</inf>O<inf>3</inf> (Ni/La<inf>2</inf>O<inf>3</inf>), which enables efficient CO<inf>2</inf> methanation at room temperature using LaNi<inf>5</inf> and H<inf>2</inf>/CO<inf>2</inf> mixed gas as source materials. The experimental findings assuredly corroborate that CO<inf>2</inf> methanation proceeds through the formate route in the LaNi<inf>5</inf>-[CO<inf>2</inf>+H<inf>2</inf>] system. This pathway involves the absorption of H<inf>2</inf> by LaNi<inf>5</inf>, dissociation of hydrogen atoms, and their reaction with the formed La<inf>2</inf>O<inf>3</inf> to generate surface hydroxyl groups. These hydroxyl groups play a crucial role in facilitating the dissociative adsorption of CO<inf>2</inf> on La<inf>2</inf>O<inf>3</inf>, resulting in the formation of carbonate and bicarbonate intermediates. Subsequently, these intermediates are continuously hydrogenated by the hydrogen atom flux from LaNi<inf>5</inf>H<inf>x</inf>, ultimately producing formate and methane. Our experimental and computational results demonstrate that modulating a metallic Ni active site center through direct interaction with a La<inf>2</inf>O<inf>3</inf> support and exposing CO<inf>2</inf> to active hydrogen atoms sourced from metal hydrides may be a powerful strategy for promoting novel reactivity paradigms in CO<inf>2</inf> catalytic reduction reactions.