Date of Award
Master of Science
Chemical and Biological Engineering
Luke T. Roling
Modeling chemical reactions in the condensed phase has been of increasing interest in recent studies due to the large range of relevant reactions (e.g. biomass conversion). Recently, some studies in the condensed phase through computational approaches have been reported, utilizing implicit, molecular dynamics (MD) and ab-initio molecular dynamics (AIMD) methods for treating the solvent. However, calculations of reaction energetics in condensed phase are more challenging than in gas phase reactions, because they require expensive computational cost to consider effects of many solvent molecules. From the point of view of catalyst design, efficient and simple methods are necessary to screen a number of catalyst candidates and to save cost for calculations involving complex reaction networks.
Scaling approaches in gas phase have successfully estimated reaction energetics of a variety of systems. We believe that this well-developed method can also work well in condensed phase. In this study, we established scaling relations for adsorption energies of hydrogenated O, C, N, and S with various solvent representations, using adsorption energies of single adatom as descriptors. We investigated effects of a single water molecule, a methanol molecule, two water molecules, ice-like structure and disordered water configuration on 〖∆E〗_ads using density functional theory (DFT). Seven different types of transition metals, Cu, Ag, Au, Pd, Pt, Ir and Rh, were tested as substrates. Structure sensitivity of scaling relation was studied using fcc(111) and (100) facet as well. As a result, the linear properties of scaling relations were preserved in all solvent representations we tested. The slope of scaling relation in the condensed phase did not change significantly compared to that in the gas phase, but intercept was shifted due to the formation of H-bonds between adsorbate and water. Investigations of the electronic states of the metal surface suggest that bond order conservation still dictated slopes of scaling relations in condensed phase since adsorbed water has minimal effect on the d-states of the surface metal atom which adsorbate was placed on. We believed these scaling relations show the potential of this approach to efficient screen catalysts for condensed phase reactions.
Park, Jaeryul, "Elucidating energy scaling relations between simple atomic and molecular adsorbates in the presence of solvent" (2019). Graduate Theses and Dissertations. 17764.