Adsorption properties of HKUST-1 toward hydrogen and other small molecules monitored by IR

Abstract

Among microporous systems metal organic frameworks are considered promising materials for molecular adsorption. In this contribution infrared spectroscopy is successfully applied to highlight the positive role played by coordinatively unsaturated Cu²⁺ ions in HKUST-1, acting as specific interaction sites. A properly activated material, obtained after solvent removal, is characterized by a high fraction of coordinatively unsaturated Cu²⁺ ions acting as preferential adsorption sites that show specific activities towards some of the most common gaseous species (NO, CO₂, CO, N₂ and H₂). From a temperature dependent IR study, it has been estimated that the H₂ adsorption energy is as high as 10 kJ mol⁻¹. A very complex spectral evolution has been observed upon lowering the temperature. A further peculiarity of this material is the fact that it promotes ortho–para conversion of the adsorbed H₂ species.