Mechanistic insights into the CO₂ capture and reduction on K-promoted Cu/Al₂O₃ by spatiotemporal operando methodologies

Abstract

Integrated CO2 capture and conversion processes bring the promise of drastic abatement of CO2 emission together with its valorisation to chemical building blocks such as CH4 and CO. Isothermal CO2 capture and reduction (CCR) on a K-promoted Cu/Al2O3 was recognised as an effective catalytic strategy for removing CO2 from diluted stream and converting it to syngas (H2 + CO) employing green H2 as reducing agent. The dual functionality of the catalyst is the key of this dynamic process, in which the alkaline metal introduces the capture functionality and copper ensures the selective conversion of the captured CO2 to CO. However, the highly dynamic state of the catalyst at reaction conditions represents a barrier for the identification of the catalytic mechanism of CCR, which is vital for rational process improvement and design. In this work, we conducted a mechanistic investigation of CCR by means of spatiotemporal operando methodologies, gaining insights into dynamic variation of temperature, gas concentration and reactive surface species in the CCR reactor. The results show the unique potassium state exothermically captures CO2 as surface carbonates which can be reduced to CO rapidly under H2 atmosphere. When the surface carbonates are transformed to formates the reaction path is altered and the reduction to CO becomes slower. By designing controlled catalytic experiments, we further demonstrate the active involvement of CO in the capture mechanism and the effectiveness of CO2 capture in presence of an oxidised surface, extending the perspectives and suitability of CCR to treat actual complex effluent streams.