BH4 Reduction of CO2

Biomimetic hydride transfer catalysts are a promising route to efficiently convert CO2 into more useful products, but a lack of understanding about their atomic-scale reaction mechanisms slows their development.

One such reaction is using borohydride (BH4) for a hydride transfer to CO2. We obtained reactant and product states of the reaction from high-temperature Born-Oppenheimer molecular dynamics (BOMD) of this reaction. Two chain-of-state methods were used to identify reaction pathways: NEB and single-ended GSM. First, we used the high-temperature BOMD structures to obtain a 0 K NEB pathway of the reaction. Second, we used a global optimization code, ABCluster, to identify initial structures for a single-ended growing string method calculation. These two methods provide potential reaction pathways for BH4 reduction of CO2 at 0 K. To examine solvent effects at different levels of theory, we replaced specific portions of the explicit solvent molecules with different dielectric continuum (SMD, PCM, COSMO, CANDLE, etc.) or hybrid (COSMO-RS, ESM-RISM) solvent models. Furthermore, we investigated the role of counter ions in reaction energetics and solvent models.

Since chain-of-state methods provide pathways at 0 K we also used umbrella sampling with BOMD to obtain a potential of mean force (PMF) of the reaction. This PMF simulation can provide even more physical insight into the reaction with dynamic (thermal) contributions at a significant computational cost. We found that the pathways are generally similar, but not always. The PMF energies are not always consistent with chain-of-state methods using continuum or hybrid solvent models. This points towards needing guidelines of when PMF simulations are necessary or when it can be confidently ignored.


Alex Maldonado, Mitch Groenenboom

Groenenboom et al., Chem. PHys. Chem., 2017, 18, 22, 3148-3152, DOI: 10.1002/cphc.201700608.
Groenenboom et al., J. Phys. Chem. B, 2016, 120, 41, 10797-10807, DOI: 10.1021/acs.jpcb.6b07606.
Grice et al., Fuel, 2015, 150 DOI: 10.1016/j.fuel.2015.02.007.