Investigation of ethene adsorption on Hmordenite and modified Hmordenite by frequency response method

The frequency response (FR) technique has been applied to study adsorption mechanism of ethene in parent Hmordenite (HMor) and the HMor (CuO/HMor, Cs⁺/HMor) which were modified by CuO and Cs⁺. The FR spectra of ethene in HMor, CuO/HMor and Cs⁺/HMor were recorded at temperatures between 252 and 273 K under the pressure of 0.2-30.0 Torr, and then those FR spectra were investigated. The results showed that two parallel adsorption processes exist in ethene/HMor system. Those two processes were attributed to adsorption process of ethene on proton acid sites (low frequency adsorption) and on hydrogen cation sites (high frequency adsorption); meanwhile the number of sites available for adsorption of ethene is 0.692 and 0.828 mmol g⁻¹, respectively. The number of adsorption sites in low frequency is increased by the introduction of CuO which is located among the proton acid sites but covered the hydrogen ion sites in high frequency. Chemical adsorption of ethene is the main sorption process in CuO/HMor. The number of adsorption sites in low frequency is decreased by the introduction of Cs⁺ which counteracted proton acid sites in low frequency. Physical adsorption is the main sorption process in Cs⁺/HMor channels. The optimum content of CuO for modification is 5% (weight/weight). Combining the FR spectra and other methods such as isotherms and Langmuir model, a thorough understanding of the ethene adsorption processes on zeolites can be achieved.