Synthesis of A- and H-type Zeolites from Fly Ash and Their Adsorption Mechanisms for SO2, CO2, and NO

• • A-type zeolite synthesized from fly ash exhibits a specific surface area of 18.59 m2/g and pore size of 3–5 nm, achieving saturated adsorption capacities of 1.07 mmol/g (SO2), 0.26 mmol/g (CO2), and 0.048 mmol/g (NO) at 1000 mg/m3 and 20 °C; these values are critical for designing low-concentration flue gas treatment systems. • • H-type zeolite, with a higher surface area of 22.32 m2/g, outperforms A-type, reaching 1.12 mmol/g (SO2), 0.29 mmol/g (CO2), and 0.053 mmol/g (NO) under identical conditions, indicating that surface area and silanol density are decisive for acidic gas uptake. • • In-situ DRIFTS identifies T–O (T=Si/Al) groups as the primary adsorption sites; adsorption energies for A-type zeolite are -5.11 kJ/mol (SO2), -4.07 kJ/mol (CO2), and -1.41 kJ/mol (NO), confirming physisorption and guiding future modification strategies. • • Kinetic data fit the Arrhenius equation, enabling prediction of temperature-dependent adsorption rates; this is essential for scaling up to industrial flue gas conditions where temperature varies.