Stable Three-Dimensional Macroporous Iron-Foam Catalyst for Direct Conversion of CO₂ to Olefins

Abstract

The direct conversion of CO 2 using renewable powergenerated hydrogen is an approach to the production of high-value olefins. However, achieving a high-level catalyst that has high activity/ selectivity and especially good stability is still challenging due to the limitations in both thermodynamics and kinetics. Herein, we report a self-supported catalyst system composed of highly conductive iron foam substrate and in situ generated surface iron oxide layer coupled with promoter (Mn and K) nanoparticles. At industrially relevant conditions, this macroporous catalyst achieves C 2+ olefin yield as high as 29.6%, with a selectivity of 77%, and with >40% CO 2 conversion and a very low selectivity of undesired CO (5.5%). More strikingly, it enables direct conversion of CO 2 with remarkable stability for >1000 h on stream at high weight hourly space velocity. The special iron foam self-supported structure ensures the highly efficient intersite synergy of reverse water−gas shift path over Fe 3 O 4 sites and subsequently Fischer− Tropsch synthesis path over iron carbides. In situ characterizations together with density functional theory calculations demonstrate that the presence of multiple interfacial sites and addition of promoters (Mn and K) enhance the C−C coupling reaction and inhibit the undesired CO 2 methanation or olefin secondary hydrogenation. The unique and stable structure of this catalyst renders iron foam a promising industrial catalyst system for directly converting CO 2 into chemicals.