Consequences of cavity size and palladium addition on the selective hydrogen adsorption in isoreticular metal-organic frameworks

The effect of Pd-doping on the adsorption properties of three isoreticular metal-organic frameworks (IRMOFs), presenting different cavity sizes (IRMOF-1, IRMOF-8 and IRMOF-10), has been studied in this work. Parent IRMOFs were synthesized and doped with palladium by incipient wetness impregnation. The resulting materials were characterized by XRD, N2-phsyisorption, TEM and temperature-programmed decomposition. The effect of Pd incorporation on H2 and CO2 adsorption was evaluated by thermogravimetry. Hydrogen uptake is favored by the spillover effect, although the partial blockage of micropores, and structural changes in the MOF structure hinders hydrogen adsorption. In the case of carbon dioxide, it is observed an enhancement on the adsorption after palladium impregnation attributed both to morphological changes, and to the modification of electronic charge of the ligands aromatic structures. As result, the H2/CO2 adsorption capacity ratio increases after palladium impregnation only for Pd-IRMOF-8, leading to a promising material for hydrogen separation and storage.