In-situ synthesis of [Ni(tzba)0.5(F)(bpy)] membrane with high H2 permeability through ultramicropores and selective CO2 adsorption with strong affinity of uncoordinated N-Ni-F− active sites

Abstract

To simultaneously purify H2 and capture CO2 in the steam methane reforming (SMR) process for H2 production, a bifunctional metal organic framework (MOF) membrane ([Ni(tzba)0.5(F)(bpy)]) was proposed via an in-situ synthesis method to efficiently permeate H2 through ultramicropores and selectively adsorb CO2 with the strong affinity of uncoordinated N-Ni-F− active sites. Ni(tzba)0.5(F)(bpy) exhibited a good CO2 uptake capacity (4.3 mmol/g at 273 K and 110 kPa) because the F− anionic and exposed uncoordinated tetrazolate N atoms in ligands have an excellent affinity to CO2. Dynamic breakthrough experiments suggested that Ni(tzba)0.5(F)(bpy) achieved efficient separation of CO2 from H2, CH4, and N2. Ni(tzba)0.5(F)(bpy) MOF membrane also shows outstanding H2/CO2 separation performance because the high adsorption capacity of CO2 reduced CO2 mobility. The H2 permeability of 1.59 × 105 Barrer and H2/CO2 ideal selectivity of 14.43 greatly exceeded the latest upper bound. Continuous permeability tests of up to 100 h demonstrated the long-term stability of the Ni(tzba)0.5(F)(bpy) MOF membrane for H2 separation applications. Density functional theory (DFT) calculations clarified the adsorption mechanism of Ni(tzba)0.5(F)(bpy) towards gases.