Reactive direct air capture of CO2 to C–C coupled products using multifunctional materials

Abstract

Current direct air capture (DAC) approaches require a significant amount of energy for heating CO₂-sorbed materials for regeneration and for compressing CO₂ for transportation purposes. Rationally designing materials offering both capture and conversion functionalities could enable more energy and cost-efficient DAC and conversion. We have developed a single sorbent-catalytic (non-noble metal) material for the Integrated Direct Air Capture and CATalytic (iDAC-CAT) conversion of captured CO₂ into value-added products. Solid sorbents are integrated with catalytic components to first capture CO₂ from air. Subsequently, captured CO₂, with renewable H₂ co-feed is converted into olefins and paraffins. To the best of our knowledge, this is the first proof-of-concept demonstration for production of C₂ products such as olefins from captured CO₂. Among the different sorbent-catalytic materials studied, Fe/K₂CO₃/Al₂O₃ showed the best performance for integrated CO₂ capture and conversion to C₂ products. CO₂ capture capacity of 8.2 wt% was achieved under optimized capture conditions at 25 °C, and a conversion of >70% to paraffins and olefins was achieved at 320–400 °C. The hydrogenation of captured CO₂ was facilitated by the in situ formation of Fe₃O₄ and Fe₅C₂ species. The proximity between K and Fe was identified to be critical for producing C₂ products from the captured CO₂. The preliminary technoeconomic and life-cycle assessments suggest that the cost of the DAC can be considerably decreased by adopting the suggested iDAC-CAT technology, while renewable olefins could potentially be produced with negative greenhouse gases emissions.