Composition-dependent catalytic transition in NixMg1-xO via reduction-driven surface reorganization for low-temperature CO2 methanation

Abstract

CO2 methanation is a key reaction for carbon recycling and renewable energy storage, yet low-temperature performance remains highly sensitive to the surface structure of Ni-based catalysts. In Ni–MgO systems, the catalytic role of composition is often discussed in terms of a gradual metal-loading effect, although under reducing conditions, the surface can reorganize and redefine the accessible active-site configurations. Here, we report that co-precipitated NixMg1-xO catalysts undergo a composition-dependent catalytic transition, enabled by a structurally integrated Ni–O–Mg mixed-oxide framework. Systematic tuning of catalytic composition identifies a distinct threshold between x = 0.52 and x = 0.77 over NixMg1-xO, across which the reduced surface state changes sharply. Below the threshold, Ni remains largely embedded in the mixed-oxide matrix, while the exposure of metallic Ni0 sites is negligible. Above the threshold, however, enhanced reducibility drives surface reorganization, resulting in Ni redistribution and the emergence of Ni0 domains alongside residual Ni–O–Mg environments, thereby creating abundant Ni0–oxide interfacial sites. This reorganized surface promotes dissociative H2 activation and restructures CO2 adsorption states, thereby driving a mechanistic shift from the formate pathway to a CO-mediated hydrogenation pathway. Consequently, the Ni-rich catalyst (x = 0.96) shows outstanding performance with XCO2 = 94.1% and SCH4 = 100% at 250 °C. Overall, these results highlight threshold-triggered surface reorganization as a key design principle for developing NixMg1-xO catalysts with high low-temperature methanation performance. © 2026 Elsevier B.V.