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

Abstract

This study explored the integration of NaCl-CaCl 2 molten solar salts with CaO in the integrated CO 2 capture and utilization via reverse water gas shift reaction (RWGS). It was demonstrated that the molten salt system significantly improves CO 2 capture capacity and CO generation rate compared to CaO alone. The system achieved a CO 2 conversion of 56.99 % at 650 ℃, with a notable average CO 2 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-CaCl 2 -CaO was found to be the main reason for enhancing CO 2 capture through the TG-DSC test. XPS analyses confirmed that the eutectic melting of the salts disrupts the crystalline structure of CaO, leading to CO 2 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 CO 2 capture and conversion molten salt systems. • Enhanced ICCU performance : NaCl-CaCl 2 molten salts with CaO achieve 56.99 % CO 2 conversion at 650 ℃. • Mechanistic Insights : Eutectic melting disrupts CaO structure, enhancing CO 2 capture and CO generation. • Industrial Potential : Solar-driven CaO-NaCl-CaCl 2 system offers promising industrial CO 2 conversion.