A green approach to CO2 capture using fly ash-based catalysts: Performance and mechanistic insights

• Fly ash functionalized with Fe 2 O 3 and Al 2 O 3 to catalyze CCUS desorption process. • Functionalized fly ash reduced energy consumption by 43.6% in desorption. • Machine learning analyzed key catalyst features and their SHAP values. • Experiments confirmed the catalyst features highlighted by machine learning. • Acid and basic sites on functionalized fly ash synergistically enhance CO 2 release. Fly ash (FA), an abundant industrial by-product, has emerged as a promising catalyst for regenerating liquid sorbents used in CO 2 capture, significantly reducing the overall energy consumption of the process. Considering that the primary metal oxides in FA − Fe 2 O 3 and Al 2 O 3 − provide Brønsted and Lewis acid sites critical for enhancing CO 2 release, this study explores the development of modified catalysts by loading additional amounts of these metal oxides onto FA (resulting in Fe 2 O 3 -FA and Al 2 O 3 -FA), aiming to further improve FA-catalyzed CO 2 desorption. The performance of these catalysts was examined in desorption of a CO 2 -loaded MEA solution, focusing on key metrics such as CO 2 desorption rate, cyclic capacity and heat duty. Our findings indicate that modifying FA with metal oxides increases its surface acidity (both Brønsted and Lewis) and optimizes acid/alkali strength. Among the catalysts tested, Al 2 O 3 -FA exhibited superior performance, achieving a higher CO 2 desorption rate, greater cyclic capacity, and lower heat duty compared to Fe 2 O 3 -FA, unmodified Al 2 O 3 and FA, and the uncatalyzed system. Additionally, the stability of Al 2 O 3 -FA was confirmed over 20 continuous repetitions of CO 2 capture and desorption, finding no significant alteration in catalytic activity or material structure (as confirmed by FT-IR and XRD characterization) after prolonged use. The machine learning also was used to correlate the catalysts features and performance while the importance of each feature was identified. Finally, a potential catalytic reaction mechanism is proposed, involving the deprotonation of MEAH + and decomposition of MEACOO − , both of which synergistically enhance CO 2 desorption during sorbent regeneration process.