Date of Award
Open Access Dissertation
Liquid phase processing is often desired for selective product formation, such as during catalytic conversion of biomass, and for purification of waste-water streams. Since the liquid phase environment influences the adsorption properties and reactivity of solid catalysts and porous materials, significant performance changes have been observed as a function of solvent properties for various industrial catalytic and separation processes. There is a need to better understand these solvation effects on processes at solid-liquid interfaces and to develop novel multiscale models that permit one to explore solvation effects on surface catalyzed reactions and during adsorption in porous media such as zeolites. It is these tasks that this thesis addresses.
Specifically, the objective of our initial study is to identify the active site and understand the various solvation effects for the hydrodeoxygenation of organic acids derived from biomass over Pd catalysts to produce green diesel. This investigation finds that independent of solvent environment the Pd(100) surface is 3-7 orders of magnitude more active than the most dominant Pd(111). The presence of liquid water inhibits the most relevant decarbonylation mechanism and although decarboxylation is accelerated by the presence of water, over Pd catalysts the decarbonylation mechanism is the only relevant deoxygenation pathway.
We then developed an explicit solvation method based on a hybrid quantum mechanical and molecular mechanical (QM/MM) description of the total reaction system understand site-specific solvation effects on the adsorption behavior of molecules in porous materials such as zeolites. The developed method overcomes the conceptual limitations of both implicit solvation methods and classical force field methods. To test and validate our hybrid QM/MM-FEP (Free Energy Perturbation) technique, we studied methanol and ethanol adsorption at the acid sites in zeolite H-MFI in both the gas phase and in liquid water. Our explicit solvation calculations predicted an exergonic solvation free energy of adsorption for both methanol and ethanol, which is consistent with experimental data.
Finally, we applied our novel QM/MM-FEP method to study solvation effects on the adsorption characteristics and removal of sub-ppm level contaminants of emerging concern (CECs) such as clofibric acid, aspirin, and bisphenol A from waste-water streams with the help of nano-porous adsorbents. We found that in H-MFI zeolite all studied CECs exhibit an exergonic solvation effect during adsorption. In other words, the presence of liquid water increases the selectivity of the adsorbent to remove the CECs from water.
Kundu, S. K.(2022). Liquid Phase Modeling in Metal Catalysis and in Zeolites. (Doctoral dissertation). Retrieved from https://scholarcommons.sc.edu/etd/7037
Available for download on Friday, December 15, 2023