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Vapor-phase treatment of ZIF-8 membranes with manganese(II) acetylacetonate (Mn(acac)2 ) allows permselectivity tuning. Propylene/propane selectivity increases from 31 to 210 after the Mn(acac)2 treatment at 165 °C for 30 min, while selectivities increase from 14.6 to 242 for H2 /CH4 , from 2.9 to 38 for CO2 /CH4 , from 2.4 to 29 for CO2 /N2 , and from 2.9 to 7.5 for O2 /N2 , after Mn(acac)2 treatment at 175 °C for 30 min. Stable equimolar propylene/propane mixture selectivity of 165 at ambient temperature and 4 bar equimolar feed with a propylene flux of 8.3×10-4 mol m-2 s-1 is established. A control experiment excludes thermal treatment alone causing these changes. XPS analysis reveals the presence of Mn(acac)2 on the outer surface of the vapor-treated ZIF-8 membranes while no other changes are detectable by X-ray diffraction and infrared spectroscopy.
Hayashi et al. (Sat,) studied this question.