Research progress on spinel-catalyzed CO₂ hydrogenation to methanol

The synthesis of green methanol from CO₂ and green hydrogen represents a crucial pathway for achieving carbon cycling and energy structure transition. However, high-efficiency catalysts remain the bottleneck hindering its industrialization. Spinel oxides （AB₂O₄） are ideal materials for catalyzing CO₂ hydrogenation to methanol due to their cation exchangeability, structural robustness, and surface acid-base synergy. This review systematically summarizes the research progress on the structure-activity relationships and modification strategies of spinel catalysts. Firstly, the reaction mechanism of CO₂ hydrogenation over spinel catalysts is analyzed. It is revealed that the CO₂ activation mechanism relies on electron transfer mediated by surface oxygen vacancies （O_v） and the synergistic effect of the inherent Lewis acid-base pairs （Mⁿ⁺−O²⁻）. Concurrently, H₂ activation on spinel catalysts occurs via heterolytic dissociation pathways, with the O_v concentration, electronic structure of the metal centers, and the synergistic effect of Mⁿ⁺−O²⁻ pairs influencing the H₂ activation energy. The reaction pathway mainly involves two competitive routes: the formate pathway and the reverse water-gas shift coupled with CO hydrogenation pathway （RWGS + CO hydrogenation）. Secondly, spinel catalysts modification strategies are summarized, including precise regulation of oxygen vacancies, synergistic optimization of coordination-electronic structures, synergistic reinforcement of active metal-spinel interfaces, and the construction of spinel-zeolite tandem catalysts. O_v regulation and coordination-electronic structure modification are achieved through strategies such as element doping, reduction pretreatment, and facet exposure. High-density surface O_v enhances CO₂ adsorption and activation, promoting the formate pathway. The synergistic effect between active metals and spinel is realized by constructing a strong metal-support interaction （SMSI）, enabling spatial compartmentalization of H₂ dissociation at metal sites and CO₂ activation at spinel sites, effectively suppressing side reactions. The pathway selection in CO₂ hydrogenation to methanol over spinel catalysts is not a static process but is dynamically regulated by surface composition, defect structure, metal synergy, and reaction conditions. Spinel systems exhibit excellent selectivity and stability advantages in the CO₂-to-methanol reaction; however, their long-term stability under impurity-containing gas sources requires further exploration, and the space-time yield （STY） under mild conditions remains an engineering bottleneck. Future research should focus on stability against gas impurities and anti-poisoning design, synergy between in situ/operando characterization and micro kinetics, directional regulation of active sites/structures, quantification and reversible control of interface engineering, and synergistic optimization of tandem catalysis and reaction engineering. Through the core regulatory framework of “defect-coordination-interface”, breakthroughs in the performance of spinel catalysts for CO₂ hydrogenation to methanol can be achieved. This review aims to elucidate the structure-activity relationships between catalyst structure and reaction pathways at the atomic level, providing theoretical guidance for designing high-performance spinel catalysts.