Mechanisms of using NaCl-CaCl₂ molten solar salts in enhancing the integrated CO₂ capture and utilization via reverse water gas shift (ICCU-RWGS) process with CaO alone

This study explored the integration of NaCl-CaCl₂ molten solar salts with CaO in the integrated CO₂ capture and utilization via reverse water gas shift reaction (RWGS). It was demonstrated that the molten salt system significantly improves CO₂ capture capacity and CO generation rate compared to CaO alone. The system achieved a CO₂ conversion of 56.99 % at 650 ℃, with a notable average CO₂ capture rate of 0.64 mmol g⁻¹ min⁻¹ and CO generation rate of 0.23 mmol g⁻¹ min⁻¹. The co-melting behavior of NaCl-CaCl₂-CaO was found to be the main reason for enhancing CO₂ capture through the TG-DSC test. XPS analyses confirmed that the eutectic melting of the salts disrupts the crystalline structure of CaO, leading to CO₂ and metals bonding through adsorbed oxygen rather than lattice oxygen. Combined with the mechanistic insights provided by in-situ DRIFTS and in-situ Raman, it was confirmed that the easier desorption of adsorbed oxygen is the key factor behind the enhanced CO generation during the RWGS stage in the molten salt environment. These findings provide foundational insights for the future design of solar-driven CO₂ capture and conversion molten salt systems.