Evaluation of Iron-Based Metal-Organic Framework Activation Temperature in Acetylene Adsorption

One of the major issues regarding long-term human space exploration is the need for a breathable atmosphere. Typically, this requires both removal of exhaled CO2 and generation or recovery of oxygen. NASA’s current technology only operates at about 50% efficiency due to the need to vent methane that is produced during the CO2 reduction process. One method of improving the efficiency of this process is through plasma pyrolysis, wherein the methane is pyrolyzed to produce hydrogen and various dehydrogenated carbon byproducts, with acetylene being one of the main components of this byproduct stream. Unfortunately, while the concentration of this effluent is generally high in hydrogen (>90% typically) the presence of this acetylene can act as a poison for the Sabatier catalysts, requiring a removal step. Metal-organic frameworks (MOFs) represent a valuable method removing these unsaturated hydrocarbons due to their high tunability, particularly through the incorporation of open metal sites. In this study, two common iron-based MOFs, MIL-100 and PCN-250, were studied for their ability to adsorb acetylene. A combination of gas adsorption and density functional theory results show the ability of these materials to undergo a thermal induced reduction event results in an improvement in gas adsorption performance, which appears to be at least partially due to the increased presence of π-backbonding towards the acetylene molecules.