FTIR spectroscopy and thermodynamics of hydrogen adsorbed in a cross-linked polymer

The adsorption of H-2 in a cross-linked poly(styrene-co-divinylbenzene) (St-DVB) microporous polymer ( BET surface area 920 m(2) g(-1)) is studied by volumetric and gravimetric methods, FTIR spectroscopy at variable temperature ( 300-14 K) and ab initio calculations. At 77 K the polymer reversibly stores up to 1.3 mass% H-2 at a pressure of 1 bar and 1.8 mass% at 10 bar. The adsorption process involves the specific interaction of H-2 with the structural phenyl rings through weak dispersive forces. The interacting molecules become IR active and give rise to vibrational and rotational-vibrational manifestations which are affected by the temperature, the contact time and the H-2 equilibrium pressure. The spectra of the H-2/St-DVB system reported here represent the first IR evidence of the adsorption of hydrogen on unsaturated molecules. The adsorption enthalpy is evaluated by the VTIR ( variable temperature IR spectroscopy) method ( C. Otero Arean et al., Phys. Chem. Chem. Phys., 2007, DOI: 10.1039/b615535a) and compared with the results of ab initio calculations for the H-2/benzene interaction and with literature data.