Abstract: The frequency response (FR) technique were applied to study adsorption mechanism of ethene on parent mordenite and the mordenite modified by CuO and Cs+. The FR spectra of ethene on parent mordenite and modified mordenite were recorded and analyzed at temperature of 252 and 273 K and in the pressure range of 26.6-3990 Pa. The results showed that adsorption of ethene was the rate controlling step and there were two parallel adsorption processes in ethene/parent mordenite system. Those two processes were attributed to adsorption process of ethene on proton acid sites (low frequency adsorption) and on sodium cation sites (high frequency adsorption), and the numbers of sites available for adsorption of ethene were 0.692 and 0.828 mmol·g-1, respectively. The number of adsorption sites in low frequency adsorption was increased by the introduction of CuO, which was located among the proton acid sites and covered the sodium cation sites in high frequency adsorption. Chemical adsorption was the main sorption process in mordenite channels modified by CuO. The number of adsorption sites in high frequency adsorption was increased by the introduction of Cs+, which counteracted proton acid sites in low frequency adsorption. Physical adsorption was the main sorption process in mordenite channels modified by Cs+. The effective mass fraction of CuO for modification was 5%. The ethene adsorption processes on zeolites can be studied in detail by combining the FR spectra, isotherms, and Langmuir model.

Key words: Frequency response, Ethene, Mordenite, Relaxation time, Adsorption site