Efficient conversion of CO2 into valuable chemicals has the potential to reduce net CO2 emissions while generating fuels and other commodities. However, hydrogenation of CO2 is very challenging due to its chemical inertness and thermodynamic stability. Frustrated Lewis pairs (FLPs), which are molecules having both Lewis acid and base sites in a single molecule, can both bind CO2 and heterolytically dissociate H2, which shows great potential in CO2 hydrogenation. However, FLPs are homogeneous catalysts that have considerable disadvantages compared with heterogeneous catalysts, such as difficulty with catalyst recycling and product separation. In this work we design novel CO2 hydrogenation catalysts in silico that combine the advantages of both homogeneous and heterogeneous catalysts. Our approach is to functionalize metal organic frameworks (MOFs) with a series of different Lewis pairs (LPs) to create heterogeneous catalysts. We employ UiO-66 as base MOF because it is chemically and thermally stable, is highly selective toward CO2 and can be readily functionalized. We have designed a family of LP functional groups for functionalization of UiO-66 and evaluated these materials by computing binding energies and reaction pathways for CO2 hydrogenation from density functional theory (DFT). We found that CO2 hydrogenation proceeds via a two-step process, with the first step being heterolytic H2 dissociation and the second step being a 2-electron reduction of CO2 via concerted hydride and proton attachment. We have identified linear energy relationships for the CO2 hydrogenation barriers and H2 dissociation barriers that allow for efficient screening of the catalytic activity of potential catalysts. Our DFT calculations indicate that these materials should be stable and have significant activity at moderate temperatures and pressures for producing formic acid from CO2 and H2. We have also designed new catalysts for CO2 hydrogenation to produce methanol based on UiO-67 on insight derived from our UiO-66 studies.

Design of Lewis pair-functionalized metal organic frameworks for CO2 hydrogenation

251st National Meeting (2016)

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