Speaker
Description
The metal-organic frameworks (MOF) are a new class of porous materials that have high potential for carbon capture and storage (CCS). CPO-27-Mg (Mg-MOF-74) is one such MOF that has under-coordinated Mg2+ sites where $\mathrm{CO}_2$ gas molecules can bind selectively at low partial pressure (below 1 bar). Prerequisite to a rational design of improved material with optimized separation conditions is the reliable prediction of co-adsorption equilibria. Generic force fields, which have often been employed in classical Grand Canonical Monte Carlo (GCMC) simulations to forecast co-adsorption of gas mixtures, are found to be inadequate in describing the molecule-surface interactions in MOFs with open metal sites. Although the tedious ab initio parametrization of force fields improve the description, these standard GCMC simulations still neglect the zero point vibrations (ZPV) and framework relaxation (FR) effects on adsorption.
We developed an alternative GCMC simulation methodology [1], which utilizes Gibbs free energies of adsorption of individual sites and the lateral (adsorbate–adsorbate) interaction energies obtained from ab initio calculations, which define the Hamiltonian of the coarse-grained lattice-gas description of the adsorbent surface. The former includes the ZPV and FR effects, whereas the latter can be treated exactly in the proposed scheme, which avoids cumbersome fitting of the force field parameters. The possibility of applying very accurate quantum chemical methods for lateral interactions or Gibbs free energies of the individual sites makes it a powerful tool for benchmarking standard GCMC simulations.
Hybrid MP2:(PBE+D2)+ΔCCSD(T) schemes, which were shown to produce accurate Gibbs free energies (within 1 kJ/mol) [2-4], are used for each individual sites, whereas CCSD(T) lateral interaction energies are employed in this work. Together, they yield pure gas isotherms that are in close agreement with experiment. Our simulations reveal the importance of lateral interactions on co-adsorption of gas mixtures that are relevant to CCS.
References
[1] A. Kundu, K. Sillar, J. Sauer, J. Phys. Chem. Lett. 8, 2713 (2017).
[2] A. Kundu, G. Piccini, K. Sillar, J. Sauer, J. Am. Chem. Soc. 138, 14047 (2016).
[3] K. Sillar, A. Kundu, J. Sauer, J. Phys. Chem. C. 121, 12789 (2017).
[4] K. Sillar, J. Sauer, J. Am. Chem. Soc. 134, 18354 (2012).
