Uncovering hydrogen-to-carbon ratio for integrated CO2 capture and reverse water-gas shift reaction through MFB-TGA-MS analysis

The integrated CO2 capture and utilization via the reverse water-gas shift reaction (ICCU-RWGS) to produce CO represents a compelling pathway toward achieving carbon neutrality. However, achieving the desired hydrogento-carbon (H2/CO) ratio, particularly at 2:1, to serve as the feedstock for the Fischer-Tropsch Synthesis (FTS) process, remains a relatively unexplored area. This study employs micro-fluidized bed thermogravimetric analysis coupled with mass spectrometry (MFB-TGA-MS) alongside a particle-injecting method to investigate direct limestone hydrogenation using isolated solid materials (limestone as the reactant and Cu-Al catalyst as the bed material) under fluidized and isothermal conditions. The Cu-Al catalyst, utilized as the bed material, has demonstrated enhanced performance in the decomposition of limestone, resulting in a 4-fold increase in reaction rate compared to the inert quartz sand at 30 vol% H2 and 800 degrees C. Furthermore, at both milligram and gram scales, limestone exhibits favorable H2/CO ratios, especially at 30 vol% H2 concentration and a particle size of 150-200 mu m, achieving a 2:1 ratio, demonstrating its potential suitability for processes like FTS. Kinetic analysis, using the shrinking core model and a simplified K-L model, reveals activation energies of 185.2 kJ/mol (for limestone decomposition) and 100.3 kJ/mol (for the RWGS reaction), effectively predicting the entire reaction process. MFB-TGA-MS experiments and model calculations demonstrate effective conversion of unconverted CO2 by the Cu-Al catalyst bed material, resulting in a highly desired H2/CO ratio and in-situ CO2 conversion.