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

Abstract

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 π-complexation ability for 1-butene than Cu/MCM-41. Moreover, the adsorption ability of Fe–Cu/MCM-41 does not change very much upon H₂-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 π-complexation with olefin.