Adsorption Energies for Ten van der Waals Gases on a Zr-based Metal-Organic-Framework (MOF)

MOFs are relatively novel crystalline, high controlled porosity, very large adsorption specific area materials designed for use as catalyst support and applications to scientific and applied problems. We present measurements of adsorption isotherms of ten gases (H$_{\mathrm{2}}$, D$_{\mathrm{2}}$, Ne, N$_{\mathrm{2}}$, Ar, CO, CH$_{\mathrm{4}}$, Kr, Xe and C$_{\mathrm{2}}$H$_{\mathrm{6}})$ over a wide range of the appropriate temperatures on a Zr-based MOF$_{\mathrm{\thinspace }}$known as NU-1000 of specific area $\approx $2600 m$^{\mathrm{2}}$/gram. A first set of measurements$^{\mathrm{1}}$ was used to calculate the differential heat of adsorption over the entire monolayer range. A second set emphasized the four central atoms/molecules in the series (N$_{\mathrm{2}}$, CO, Ar and CH$_{\mathrm{4}})$ for coverages under 0.1 monolayer for which density functional calculations (DFT) of the enthalpy of adsorption at zero coverage showed considerable variations. The DFT results indicated several strong adsorption sites with energy differences amongst them large enough for experimental observation. Our results show remarkable qualitative and semi-quantitative agreement with the DFT calculations assuming a sequential filling of sites, from strongest to weaker energies.$^{\mathrm{2}}$ 1. W. Zhang et al., J. Am. Chem. Soc., 140, 328 (2018) 2. G. O. Vissers et al., J. Phys. Chem. C, (2019), in press.