Quantum Chemical Kinetics of Electrochemical Bio-Oil Upgrading

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Accurate determination of reaction rate and rate-limiting steps in an electrochemical mechanism requires knowledge of activation energy or transition state energy for each reaction step. In the context of a study based on density functional theory (DFT) search methods such as nudged elastic band (NEB), climbing image NEB (CI-NEB), and the dimer method are available to estimate the structure and energy of the transition state.[1,2] However, these methods are prohibitively computationally demanding for complex reaction systems. To overcome this, linear scaling relationships have been developed to correlate the energy of a TS or activation barrier to the initial or final reaction state.[3] This approach offers the advantage of quick estimation of transition state energy where the relationship has been defined for a specific reaction type using one of the aforementioned methods. Two methods of linear scaling relationships include Brønstead - Evans -Polyani (BEP) and Transition state scaling (TSS). BEP relationships correlate the activation energy to the reaction energy of a given step. TSS relationships correlate the TS energy to the energy of the final state. Linear scaling relationships are only viable if trends have been reported for the class of molecules, reaction, and surface of interest. Here we calculate activation free energies to predict catalyst facet-dependent rate constants for the transformation of furfural to tetrahydrofuran and 4-propylphenol to propyl cyclohexane. The activation free energies are first calculated from initial and final state free energies using previously reported linear scaling relationships. Then, zeroth order reaction rate constants are calculated for each reaction step on three facets of platinum and one ruthenium facet. The furfural hydrogenation pathway is shown to be kinetically faster than that of 4-propylphenol. These results lay the groundwork for the prediction of transient product concentration profiles for the two pathways independently and in competition. References 1. J. Klimeš, D.R. Bowler, and A. Michaelides, J. Phys.: Condens. Matter 22, 074203 (2010). doi.org/10/bphpf6 2. G. Henkelman and H. Jónsson, J. Chem. Phys. 111, 7010 (1999). doi.org/10/b5nt8x 3. J.E. Sutton and D.G. Vlachos, ACS Catal. 2, 1624 (2012). doi.org/10/f394cc

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