Date of Award
Doctor of Philosophy (PhD)
J. Will Medlin
Daniel K. Schwartz
The study of catalysis is of fundamental importance to the petrochemical industry where the fast, precise production of desired products is prized for its ability to conserve energy and save money. Here we created selective catalysts by modifying Pt/Al2O3 and Pd/Al2O3 with thiol self-assembled monolayers (SAMs), modifiers with the capacity to influence the near surface environment of the catalyst.
SAM coatings were first explored for liquid phase hydrogenation of epoxybutene (EPB) in an extension to the liquid phase of previous work performed in the gas phase. These studies indicated that while general improvements in selectivity for this reaction still occurred in the liquid phase, there were other important parameters that affected the selectivity and activity of the reaction. For example, an octadecanethiol coating did not improve the selectivity of the reaction whereas a thioglycerol coating improved the selectivity from 40% to 75% when solvated in heptane. Ethanol solvated reactions were shown to have consistently lower selectivities than reactions solvated in heptane, possibly due to increased desorption of the monolayer.
The use of alkanethiols as catalyst modifiers for liquid phase reactions was next extended to larger reactants, fatty acids, which inherently require liquid phase study due to their high boiling points. The partial hydrogenation of unsaturated fatty acids is difficult to control, but an alkanethiol coated catalyst increased selectivity of the sequential reaction pathway to monounsaturated fatty acids, a desirable result for the production of biodiesel. This effect was attributed to the ability of alkanethiol tails non-specifically restricting access to the surface for monounsaturated fatty acids.
Finally, the use of functional SAMs was explored for the liquid phase hydrogenation of α,β-unsaturated aldehydes over Pt/Al2O3 catalysts. Here, the tail ligands of the thiol modifiers were specifically chosen to selectively orient the reactant cinnamaldehyde with the catalyst surface in a manner that serves as a functional handle for controlling selectivity. The work was extended to modification of Pd/Al2O3 catalysts, which showed an increase in selectivity after thiol modification, but without ligand-specific control seen for modification of Pt catalysts. Repeated recycling of these catalysts showed a decrease in efficacy, which was subsequently stabilized by adding a coating regeneration step between recycles.
Kahsar, Karl Rudolph, "Modification of Supported Metal Catalysts with Thiol Self-Assembled Monolayers" (2014). Chemical & Biological Engineering Graduate Theses & Dissertations. 2.