Integrated high-temperature CO2 capture and conversion over mixed CaO-NaAlO2 bifunctional sorbent-catalyst using a passivation strategy

The utilization of integrated CO 2 capture and utilization methods to produce value-added fuels and chemicals represents a promising approach in addressing the global warming crisis. Nonetheless, the development of cost-effective, efficient, selective, and stable dual-functional materials still poses a significant challenge. Our conversion tests and structural characterizations reveal that coupling Ca-looping (CaL) with the reverse-Boudouard (RB) reaction using a blend of limestone, NaAlO 2 , and biochar can achieve efficient capture and in situ conversion of CO 2 . In comparison to traditional alkali-carbonate catalysts, the aluminum oxide served as a passivator, impeding the acceleration of CaCO 3 decomposition, enhancing in situ CO yield, preventing catalytic deactivation from Na component reacting with ash components, and alleviating CaO sintering. This strategy enabled exceptional CO 2 conversion efficiency (approximately 90.0 %), high CO selectivity (nearing 100 %), and stability even through multiple cycles (around 90.0 %), representing a 20 % improvement over our prior materials (limestone mixed with K 2 CO 3 -impregnated biochar). Notably, density functional theory calculations further demonstrate that the activation energy barriers for monatomic C-assisted CO 2 dissociation were lower than the desorption energy of CO 2 on the NaAlO 2 (101) surface, indicating that most of the released CO 2 from limestone can subsequently be converted into CO on the NaAlO 2 surface. Hence, this cost-effective passivation approach offers a scalable solution for closing the carbon cycle from large stationary sources without necessitating carbon sequestration.