Activation of CO2 and NH3 at interface between Ni and Mg-Al mixed oxide for CH4 synthesis

Abstract

To reduce greenhouse gas emissions and achieve a sustainable society, synthesizing methane (CH₄) from carbon dioxide (CO₂) and green hydrogen (H₂) is a promising approach. However, the limited availability of renewable energy and the challenges of H₂ transport have created a demand for CH₄ synthesis using ammonia (NH₃) instead of H₂. To realize this process, the development of highly active catalysts for the one-step synthesis of CH₄ from CO₂ and NH₃ is essential, yet effective non-noble metal catalysts remain undeveloped. Here, we report the superior activity of supported Ni catalysts based on Mg-Al mixed oxide systems. Operando DRIFTS measurements revealed that CH₄ formed at the Ni-support interface through hydrogenation of isocyanate species (*NCO) derived from reaction of CO₂ and NH₃. Promoting this hydrogenation requires both high NH₃ decomposition activity and abundant Ni-support interface sites. The Mg-Al mixed oxide support, with its moderate basicity and favorable morphology for Ni dispersion, provided these features, resulting in high catalytic activity. The catalyst developed in this study demonstrates efficient CO₂ conversion into value-added products using NH3 as a hydrogen carrier and offers a promising strategy toward a more sustainable energy system.