Advances in Fe-based catalysts for the hydrogenation of CO₂ to C₂₊ alcohols

This paper examines the recent advancements and future prospects of Fe-based catalysts in the catalytic conversion of CO₂ to higher alcohols, particularly C₂₊ alcohols. The CO₂ hydrogenation process represents a promising route for sustainable energy and chemical production, potentially mitigating CO₂ emissions while producing valuable chemicals and fuels. Regarding product output, C₂₊ alcohols, represented by ethanol, possess dual attributes of bulk chemicals and basic energy products, finding wide applications in green fuel, healthcare, and fine chemical synthesis. Compared to C₁ products, the higher energy barrier introduced by C−C coupling makes the production of C₂₊ products in CO₂ hydrogenation more challenging, necessitating rational catalyst design to enhance the performance of CO₂ hydrogenation for C₂₊ alcohol production. The effectiveness of Fe-based catalysts in CO₂ hydrogenation for C₂₊ alcohols lies in the efficient C−C coupling between -\mathrmCH_m^* species and −CH_nO* species: by controllably activating the C−O bond in the −CO* intermediate, the generation rates of -\mathrmCH_m^* and −CH_nO* intermediates are matched, thereby ensuring efficient C−C coupling and laying the foundation for promoting C₂₊ alcohol synthesis. Essentially, the adsorption and evolution processes of key reaction intermediates, −CO*, are closely related to the electronic structure characteristics of Fe-based active sites. Precisely modulating the electronic structure characteristics of Fe-based active sites is the most powerful means to achieve controllable activation of C−O bonds and efficient coupling of C−C bonds. In recent years, the main methods for regulating the electronic structure characteristics of Fe-based catalysts for CO₂ hydrogenation to C₂₊ alcohols include controlling Electronic Metal-Support Interaction (EMSI) and second element doping modification. EMSI involves electron transfer at the metal-support interface, endowing the Fe-based active site surface with electron-rich/electron-deficient characteristics, thereby serving as ideal electron donors/acceptors for target reactants. By influencing the adsorption behavior of relevant species, EMSI can accelerate or inhibit related reaction processes, ultimately enhancing the synthesis performance of C₂₊ alcohols. On the other hand, the element doping modification strategy involves doping Fe-based active sites with elements possessing special electronic properties, such as alkali metals (K, Na, Cs, etc.), transition metals (Cu, Co, Mn, Cr, etc.), and p-block elements (VIA element S, IIIA element In, etc.), to chemically modify the Fe-based active sites, affecting the electron density of Fe active centers or forming synergistic catalytic centers with diversified active sites, thereby influencing catalytic activity and selectivity. Furthermore, the review explores innovative approaches for process intensification to enhance the overall performance of Fe-based catalysts. Tandem catalysis and CO/CO₂ co-feeding have emerged as promising strategies to increase CO₂ conversion rates, C₂₊ alcohol selectivity and yield. These process intensification techniques leverage synergistic effects between different catalytic components and reaction pathways, offering new opportunities for improving the efficiency and sustainability of CO₂ hydrogenation processes. There are still some challenges to be addressed. Therefore, future work can focus on the following points: (1) Rational design of Fe-based catalysts with unique electronic structure characteristics to improve their chemical, mechanical, and thermal stability and promote their industrial application process. (2) In-depth understanding of the role of EMSI effect in enhancing the performance of CO₂ hydrogenation to C₂₊ alcohols and developing high-sensitivity EMSI characterization techniques to promote the development of related catalysis theories at the interface. (3) Development of new methods for the development of multi-component cascade high-performance Fe-based catalysts, especially multi-level coupled catalysts, including molecular sieves and multi-metal-based Fe-based catalysts, which are expected to further enhance the selectivity of CO₂ hydrogenation to C₂₊ alcohols.