Redox-buffer effect of Fe2+ ions on the selective olefin/paraffin separation and hydrogen tolerance of a Cu+-based mesoporous adsorbent

In the present work, a new mesoporous adsorbent containing ferrous/cuprous ionic species (Fe-Cu/MCM-41) has been developed for selective separation of 1-butene/n-butane. Co-impregnation of Fe2+ ions with Cu+ ions within mesopores gives superior 1-butene/n-butane separation ability. Fe-Cu/MCM-41 exhibits much higher heat of adsorption for 1-butene (-23.4 kJ mol(-1)) compared to that of Cu/MCM-41 (-11.2 kJ mol(-1)), resulting in a larger adsorption amount of 1-butene over Fe-Cu/MCM-41 (4.4 mmol g(-1) at 1 atm) than that over Cu/MCM-41 (2.8 mmol g(-1) at 1 atm). The results indicate that Fe-Cu/MCM-41 exhibits superior pi-complexation ability for 1-butene than Cu/MCM-41. Moreover, the adsorption ability of Fe-Cu/MCM-41 does not change very much upon H-2-treatment at different temperatures in the range of 273 K to 473 K, revealing the excellent hydrogen tolerance of the adsorbent. Physicochemical analyses indicated that the existence of Fe2+ species prevented the oxidation and reduction of Cu+ species during the adsorbent preparation and during the separation process in the presence of a reducing gas such as hydrogen, i.e., the Fe2+ species may act as a kind of redox buffer in the Fe-Cu/MCM-41 adsorbent for improving the chemical stability of Cu+ species that are highly effective for pi-complexation with olefin.