Microwave-Assisted Reactive CO₂ Capture with the SrCO₃-Graphite System

This study details the initial development of a microwave heat-driven reactive CO2 capture (RCC) process using the SrO/SrCO3 cycle and graphitic carbon to absorb ppm-levels of CO2 from humidified room temperature air and selectively convert it into CO. By combining first-principles density functional theory (DFT) simulations with thermogravimetric analysis (TGA) and X-ray diffraction (XRD) verification, it is demonstrated that SrO spontaneously absorbs moisture to generate Sr(OH)2 followed by Sr(OH)2*1H2O, which then can spontaneously react with atmospheric levels of CO2 to form SrCO3. The resulting SrCO3 can then react with solid carbon at elevated temperatures to selectively produce CO and regenerate SrO. Graphitic carbon is an excellent microwave absorber that can quickly generate temperatures approaching 1000 °C and then cool to room temperature within minutes, potentially allowing for integration with intermittent electricity. It is shown that using microwaves to selectively heat a mixture of graphitic carbon and SrCO3 produced CO with 85 ± 3% selectivity and stable performance over ten cycles. The rapid heating for release and room temperature CO2 uptake processes appeared to prevent performance loss from particle sintering typically observed with traditional thermal systems. These results demonstrate a new RCC approach that adds to the growing number of potential technologies available for converting CO2 to useful chemicals.