The activation of Co-MOF-74 with open metal sites and their corresponding CO/N2 adsorptive separation performance

Abstract

CO is an important raw material and the separation of CO/N2 in blast furnace gas can supply an abundant source of CO. Metal organic frameworks (MOFs) containing open metal sites are capable of selectively binding to CO over N2. However, the open metal sites easily bind to guest molecules during the preparation and activation process. In this study, typical MOFs containing open metal sites (Co-MOF-74) were used to investigate the activation behavior and corresponding CO/N2 adsorptive separation performance. To characterize the removal and decomposition of guest molecules, TG-MS and NMR analysis of MOF-74 prepared under different activation conditions were performed. During the heat and vacuum process, the guest H2O and methanol (MeOH) molecules in Co-MOF-74 were first removed at 150 °C under vacuum. The aim of high temperature activation at 300 °C is the decomposition of a small amount of bind N,N-dimethylformamide (DMF) and terminal ligands occupying the open metal sites in Co-MOF-74. In addition, H2O molecules occupy the open metal sites of Co-MOF-74 during the filtration and MeOH wash steps under air, which is accompanied by the removal of a portion of DMF. The CO adsorption (298 K and 1 bar) and the CO/N2 selectivity (Ideal adsorbed solution theory: 50:50, v/v) of Co-MOF-74 activated at 300 °C was 6.07 mmol/g and 384, respectively, which was higher than that of the other activated Co-MOF-74 samples and was attributed to the effective removal of guest molecules. Our results may guide the activation of MOFs, which contain open metal sites.