Unraveling the Role of the Reaction Environment During Oxygenate Reduction From an Atomistic Perspective
Creators: name: CHAUDHARY, NEERU
Publisher: name: Washington State University
Year: 2022
Subjects: Bio-oil
Density Functional Theory
Hydro-deoxygenation
Reaction Mechanism
Selective Hydrogenation
Solvent

description: The efforts put into this dissertation with an aim to understand the influence of reaction environment during catalytic upgrading of bio-oils via hydrogenation and hydrodeoxygenation (HDO) process. Here, we probe key reaction steps occurring respectively in HDO of phenol to benzene and hydrogenation of propanal to propanol while incorporating (1) the effects of lateral interaction on configuration and distribution of reactants and intermediates, (2) the role of carbon in metal surface on HDO reactions, (3) the influence of solvent on elementary pathways and rate-limiting step.Our DFT results suggest that the lateral interactions between aromatics such as phenol and benzene-like molecules can be parameterized using a simpler mean-field approximation allowing easy incorporation of coverage effects into microkinetic models. Furthermore, for propanal-like molecules surface crowding from reactant, intermediate, and side products have a minimal effect on the reaction energies, enabling us to eliminate such complexities from our model. Our investigation on water adsorption on a Ru and graphene layer reported that the binding energy of water becomes stronger with the increasing coverage on Ru, however, showing weak interaction on the graphene layer. This indicated that carbon-supported metal catalysts, such as Ru-C, have a strong hydration at near-zero coverage but relatively weak water-surface interactions occur upon saturation. On the other hand, presence of water in hydrogenation of propanal has not only confirmed the alteration of dominant mechanism as compared to vapor phase condition but also demonstrated the promotional effect by hydrogen-bonding stabilization of transition state and ionization of hydrogen species from H* to H+. To understand the role of carbon on metal surfaces we studied phenol deoxygenation using iron carbide catalyst. Our result suggested that carbon improves the resistance of Fe towards oxidation under HDO condition, with less likely hindering the nature of catalytic activity of pure Fe metal. Lastly, we examined C-C and C-Fe lateral interaction on Fe (100) using Lattice Gas Cluster Expansion (LG CE) model. Under the perfect lattice condition, our model identified c (2 × 2) ordered structure at ½ ML, which correlates well with previous DFT studies for carbon adsorption on iron surfaces and matches with the experimentally observed LEED structure.
description: We expect that the results from the current work will provide (1) an understanding of how reactant configuration and coverage affect the adsorption of phenols and aldehydes, (2) understanding of the synergistic effect of C-C and Fe-C interactions towards an improved HDO catalytic activity of phenolic compounds on iron carbide system, and (3) insight to solvent effect on selectivity of carbonyl reduction in aldehyde. With the fundamental understanding of the process, we will be able to construct models correlating better with experimental data.