Ab initio free energy calculations for molecule – surface interactions: gas adsorption and separation in nanoporous materials

Seminars
03.11.2019
14:30
David Wang Auditorium, 3rd floor Dalia Maydan Bldg.
Prof. Joachim Sauer

Prof. Joachim Sauer

Hershel and Hilda Rich Visiting Professorship in Applied Research 2019

 Institut für Chemie, Humboldt-Universität, Berlin, Germany

Solving surface problems such as gas separation (CO2 capture and storage by MOFs – metal-organic frameworks) or heterogeneous catalysis (hydrocarbon synthesis by zeolites) requires the reliable prediction of rate and equilibrium constants. For example, the accurate ab initio prediction of adsorption isotherms and selectivities with no other input than the atomic positions is prerequisite to a rational design of materials for gas storage, e.g. for energy carriers such as H2, and separation, e.g. removal of CO2 from CH4.

This we achieve with Grand Canonical Monte Carlo (GCMC) simulations on a lattice of adsorption sites.[1] The Hamiltonian is defined by Gibbs free energies of adsorption on individual sites and lateral interaction energies (adsorbate-adsorbate) calculated ab initio.

Based on the GCMC results a new protocol is proposed for co-adsorption selectivity prediction from known (experiment or simulation) pure component isotherms that yields improved results compared to the traditional Ideal Adsorbed Solution Theory that is almost exclusively used since 50 years. 

The ab initio prediction of adsorption (Henry) constants or reaction rate constants for systems with hundreds of atoms with an accuracy that is comparable to experiment is a challenge for computa­tional quantum chemistry. We present a divide-and-conquer strategy that departs from a potential energy surface obtained by standard density functional theory with inclusion of dispersion. The energies of the reactant and transition structures are refined by wave­function-type electron correlation calculations for the reaction site.[2,3] Thermal effects and entropies are calculated from anharmonic vibrational partition functions.[4] This methodology also yields chemically accurate (± 4 kJ/mol or less) free energies of adsorption (Henry constants) for small molecules on Brønsted sites in zeolites,[5] or on metal ion and linker sites on the internal surfaces of metal organic frameworks (MOF).[6]

 

[1]          A. Kundu, K. Sillar, J. Sauer, J. Phys. Chem. Lett. 2017, 8, 2713-2718.

[2]          C. Tuma, J. Sauer, Phys. Chem. Chem. Phys. 2006, 8, 3955-3965.

[3]          M. Alessio, F. A. Bischoff, J. Sauer, Phys. Chem. Chem. Phys. 2018, 20, 9760-9769.

[4]          G. Piccini, J. Sauer, J. Chem. Theory Comput. 2014, 10, 2479-2487.

[5]          G. Piccini, M. Alessio, J. Sauer, Y. Zhi, Y. Liu, R. Kolvenbach, A. Jentys, J. A. Lercher, J. Phys. Chem. C 2015, 119, 6128-6137.

[6]          A. Kundu, G. Piccini, K. Sillar, J. Sauer, J. Am. Chem. Soc. 2016, 138, 14047-14056.