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

The
adsorption mechanism of ethane, ethylene, and acetylene (C2Hn; 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.