Insights on the Molecular Mechanisms of Hydrogen Adsorption in Zeolites

Physisorption on microporous materials has emerged as a promising strategy to store hydrogen for use as an energy carrier. Here, we investigate adsorption of hydrogen in all-silica zeolites ITQ-29 and MFI at low temperatures using molecular simulations. Out of five existing models for hydrogen and its interactions with the zeolite, we determine that a model with hydrogen as a single uncharged Lennard-Jones center best reproduces experimental adsorption isotherms. We present a new set of Lennard-Jones parameters for this model and find that small variations in the parameters have a large impact on computed hydrogen adsorption at 77 K. Preferential adsorption sites of hydrogen in the two zeolite structures are analyzed. We investigate the effect of incorporating quantum corrections via use of a Feynman-Hibbs effective interaction potential and determine that quantum corrections are important at 25 K.