Effect of extra-framework cation in ion-exchanged ZSM-5 from rice husk ash on CO2 adsorption

ZSM-5 zeolite with high aluminum content (Si/Al = 25) was synthesized and then cation-exchanged with alkali metal , alkaline earth metal , transition metal and rare earth metal cations (Li + , Mg 2+ , Ca 2+ , Cu 2+ , Zn 2+ , La 3+ and Ce 3+ ). Crystal structure and physicochemical properties were characterized by XRD , FTIR , TGA/DTG, XRF and nitrogen adsorption-desorption measurement. CO 2 adsorption isotherms of all samples were recorded approximately 0–120 kPa at 0 °C, 30 °C and 60 °C, and they were all successfully fitted by the Toth model. The N 2 adsorption isotherm presented an approximate straight rising line, and it was perfectly fitted by the Langmuir model. In addition, the CO 2 /N 2 adsorption selectivity, Henry's law constant and the working adsorption quantity were calculated by single component CO 2 and N 2 adsorption testing. Transition metal cations Cu 2+ and Zn 2+ type ZSM-5 had the maximum adsorption quantity of 0 °C (70.24 and 74.38 cm 3 /g), and they had the maximum adsorption selectivity under high pressure and adsorption saturation conditions. The adsorption heat of all ion-exchanged samples was lower than Na-ZSM-5, and it had the approximate value at high loadings (in the range of 15.46–17.65 kJ/mol).