Spillover effect on Pd-embedded metal-organic frameworks based on zirconium(IV) and benzene 1,3,5-tricarboxylate as hydrogen storage materials

A study of Pd modified zirconium-based Metal-Organic Frameworks with trimesic acid (benzene 1,3,5-tricarboxylic acid) organic linker (H3BTC)—[Zr6O4(OH)4(O2C2H3)6(BTC)2] — (ZrBTC) as hydrogen storage materials was performed. The ZrBTC was synthesized under solvothermal condition with acetic acid as the modulator. 1, 3, 5, and 10 wt% Pd were embedded into the MOFs via wet impregnation. X-ray diffraction analysis showed that the synthesized ZrBTC have high good crystallinity with sharp characteristic peaks. Functional groups analyses using FTIR showed a significant shift from 1,722 cm−1 to 1,589 and 1389 cm−1, indicating the deprotonation of the carboxylic ligands to form coordination bonds with Zr4+ ions. The materials were thermally stable up to 400 °C according to TGA/DTA analyses. The presence of Pd metal did not cause any chemical changes in the frameworks' structure but did change the morphology and decreased the crystallinity, surface area, and porosity by 1/10, as determined by SEM and surface area analyzer. Hydrogen storage measurements showed that Pd@ZrBTC afford hydrogen adsorption up to 45 times higher than that ZrBTC which could be due to a hydrogen spillover effect. ZrBTC with 10 wt% Pd loading exhibited the highest hydrogen storage capacity of 0.56 wt% at 80 °C and 1.5 bar.