Using density functional theory, we systematically compute and investigate the binding enthalpies of 14 different small molecules in a series of isostructural metal-organic frameworks, M-MOF-74, with M = Mg, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn. The small molecules we consider include major flue gas components, trace gases, and small hydrocarbons, including H2, CO, CO2, H2O, H2S, N2, NH3, SO2, CH4, C2H2, C2H4, C2H6, C3H6, and C3H8. In total, the adsorption energetics of 140 unique systems are presented and discussed. Dispersion interactions are included via a nonlocal van der Waals density functional, vdW-DF2. Hubbard U corrections are applied to the localized d electrons in transition metals, and the impact of such corrections is assessed quantitatively. For systems for which measured binding enthalpies have been reported, our calculations lead to excellent overall agreement with experimentally determined structures and isosteric heats of adsorption. For systems that have yet to be realized or characterized, we provide quantitative predictions, establishing understanding of the role of different transition metal cations in small molecule binding at open-metal sites, and identify routes for predicting potential candidates for energy-related gas separation applications. For example, we find that Ti and V cations result in the large binding energies, twice the value expected based on pure electrostatics. We associate this behavior with the specific electronic configuration of the divalent cations and symmetry of the metal coordination site upon adsorbate binding. Additionally, we predict that Cu-MOF-74 will exhibit selectivity of CO2 over H2O and that Mn-MOF-74 can be used to separate trace flue gas impurities and toxic gases from gas mixtures. This work was supported by the Department of Energy through an Energy Frontier Research Center for Gas Separations Relevant to Clean Energy Technologies. Portions of this work were also supported by the Nanoporous Materials Genome Center, and the Molecular Foundry.

Toward rational design of small molecule adsorption in open-site metal-organic frameworks with density functional theory

249th National Meeting (2015)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.