We have used density functional theory and classical grand canonical Monte Carlo simulations to identify two functionalized metal organic frameworks (MOFs) that have the potential to be used for both CO2 capture from flue gas and catalytic conversion of CO2 to valuable chemicals. These new materials based on MIL-140B and MIL-140C functionalized with Lewis pair (acid and base) moieties, which are integrated into the framework linkers. We show that the Lewis pair functional groups are capable of catalyzing heterolytic dissociation of H2 and subsequent hydrogenation of CO2 through concerted 2-H addition. We have examined the effect of pore size and framework topology on the competitive binding of H2 and CO2. We show that the small pore size of functionalized MIL-140B stabilizes the formation of a pre-activated CO2 species and that this pre-activated CO2 has a lower overall reaction barrier for hydrogenation of CO2 to formic acid than a competing pathway in the same material that does not go through a pre-activated complex. We demonstrate that steric hindrance can potentially break energy scaling relationships, which limit the ability to optimize traditional heterogeneous catalysts, by independently changing one part of the CO2 hydrogenation pathway, without negatively impacting other parts of the pathway. Specifically, we show that steric effects can reduce the CO2 hydrogenation barrier without impacting the H2 dissociation barrier or binding energy.
Bibliographical noteFunding Information:
This work was supported by the U. S. Department of Energy (grant numbers DE-SC0004484 and DE-SC0018331). This work used the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation grant number ACI-1548562. This research was supported in part by the University of Pittsburgh Center for Research Computing through the resources provided.
© 2018 The Royal Society of Chemistry.