Light Hydrocarbon Adsorption Mechanisms in Two Calcium-Based Microporous Metal Organic Frameworks

The adsorption mechanism of ethane, ethylene, and acetylene (C₂H_n; n = 2, 4, 6) on two microporous metal organic frameworks (MOFs) is described here that is consistent with observations from single crystal and powder X-ray diffraction, calorimetric measurements, and gas adsorption isotherm measurements. Two calcium-based MOFs, designated as SBMOF-1 and SBMOF-2 (SB: Stony Brook), form three-dimensional frameworks with one-dimensional open channels. As determined from single crystal diffraction experiments, channel geometries of both SBMOF-1 and SBMOF-2 provide multiple adsorption sites for hydrocarbon molecules through C-H⋯π and C-H⋯O interactions, similarly to interactions in the molecular and protein crystals. Both materials selectively adsorb C₂ hydrocarbon gases over methane as determined with IAST and breakthrough calculations as well as experimental breakthrough measurements, with C₂H₆/CH₄ selectivity as high as 74 in SBMOF-1.