Synthesis of A- and H-type zeolites from fly ash and their adsorption mechanisms for SO₂， CO₂， and NO

Fly ash， with its high content of silicon and aluminum， has become a hot topic for synthesizing high-value-added zeolites and absorbing harmful gases. However， current research primarily focuses on using fly ash-based zeolites to adsorb high-concentration gas pollutants， with few studies addressing low-concentration gas pollutants， especially acidic gases. In this study， the adsorption performance of fly ash-based zeolites （A- and H-type） for low-concentration acidic gases （SO2， CO2， and NO） in flue gas was investigated. The saturated adsorption capacities of A- and H-type zeolites for SO2， CO2， and NO were evaluated using a fixed bed infrared combined test platform under low-concentration conditions （1000 mg/m3）， for different zeolite types， and at varying temperatures. The adsorption mechanisms of SO2， CO2， and NO by A- and H-type zeolites were studied using in-situ DRIFTS spectroscopy combined with kinetic modeling. The experimental results showed that the specific surface area and pore structure of the zeolites were the main factors affecting their adsorption performance. The adsorption energies of A-type zeolite for SO2， CO2， and NO were -5.11 kJ/mol， -4.07 kJ/mol， and -1.41 kJ/mol， respectively， indicating a significantly stronger adsorption capacity compared to H-type zeolite. The T-O （T=Si/Al ） groups on the surface of A- and H-type zeolites were identified as the key active sites for acid gas adsorption， with A-type zeolite possessing a larger specific surface area and more silanol active sites. The experimental results provide a theoretical basis for the adsorption of acidic gases by fly ash-based zeolites.