Date of Award
Master of Science
Ordered alloys have been studied frequently as catalysts in recent years because of their modified electronic and geometric structure relative to monometallic catalysts. A recent report claims that perfluorinated ligands enhance the activity and cinnamyl alcohol selectivity during cinnamaldehyde hydrogenation over low temperature synthesized Pt-Fe catalysts, however, other publications discussing supported Pt-Fe alloys report enhanced catalytic properties without the need for hydrophobic perfluorinated ligand additives. One of the objectives of this thesis is to elucidate the effects of Fe and organic capping agents on the catalytic properties of Pt-Fe alloys during cinnamaldehyde hydrogenation.
Recently, mesoporous shells were reported for three-dimensional confinement of noble metal nanoparticles and offer enhanced thermal stability compared to columnar mesoporous supports and ligand-protected nanoparticulate catalysts. We have employed this motif to elucidate the roots of enhanced activity and cinnamyl alcohol selectivity in cinnamaldehyde hydrogenation over Pt5Fex (x = 0, 1, or 2) catalysts without organic capping agents or modified with saturated or perfluorinated capping agents. We show that added Fe enhances cinnamyl alcohol selectivity under all conditions, whereas perfluorinated ligands enhance activity over Pt5Fe2 reduced at 300 ÃÂ°C and Pt5Fe reduced at 500 ÃÂ°C. We therefore believe that activity enhancements are affected by several factors, including Fe/Pt ratio, reduction temperature, ligand hydrophobicity, and support hydrophobicity, and are therefore difficult to predict.
While completing this fundamental study, we also synthesized 3D confined nanoparticles using water-in-oil microemulsions to develop a bimetallic system that is easily scalable and contains tunable metal ratios and core sizes, which is necessary for industrial applications and correlating intermetallic phases with improved results. Metal precursors were coated with microporous silica in a one-pot process, and a one-pot coating and etching procedure was employed to create a yolk-shell structure with mesopores instead. The addition of organic modifiers containing amide, carboxylic acid, and sulfonic acid functional groups was also completed to confine metal ions to the core during etching steps. Our results provide the groundwork for the development of easily scalable mesoporous yolk-shell structures with tunable metal ratios in the future.
Brashler, Kyle, "Fundamental studies and practical catalytic applications of silica encapsulated alloys synthesized using the inorganic capping agent and water-in-oil microemulsion approaches" (2015). Graduate Theses and Dissertations. 15884.