Synthetic Control and Characterization of Active Sites in Well-Defined Nanocatalysts

In the pursuit of finer mechanistic control, research in heterogenous nanocatalysis increasingly seeks to control nanomaterials at the atomic scale. This necessarily starts with synthetic control and atomistic characterization. After all, if the material cannot be made and its structure not revealed, there is no possibility of understanding the mechanism it facilitates. To this end, this dissertation presents work controlling the synthesis of nanocrystalline materials, studying these materials’ structural characteristics, and employing these materials as electrocatalysts.
Organic colloidal synthesis is used to finely control nanocrystalline products. This method relies on the binding of surfactant like ligands to mediate nanocrystalline formation. Through this technique, the synthesis of Co2P/PtM and Co2P/PdM core shell nanorods, and multi dopant M-ZrO2 nano crystalline truncated octahedron are produced. Additionally, N-heterocyclic carbenes (NHCs) are incorporated as both an expansion of traditional surface directing ligands and as a post synthetic soft chemical approach to remove traditional ligands, freeing up the surface for catalysis.
X-ray absorption spectroscopy (XAS), especially extended X-ray absorption fine structure (EXAFS) is used to determine the coordination environments of single atoms and small clusters. EXAFS was used to determine that dopants in the M-ZrO2 system are substitutionally doped and in situ experiments showed that an applied potential changed both the oxidation state and the coordination of Ni single dopants. Single crystal CeO2 superclusters were used as a support material for platinum group metals and EXAFS was able to show these metals formed various sizes of clusters, and interacted strongly with the support. This was distinct from Cu, which was able to be substitutionally doped into the CeO2 superclusters. Finally, even with a mixture of alloying products, EXAFS was able to show a sulfate treated TiO2 had a unique binding interaction with a Pt precursor which led to more controlled Pt3Sn alloyed products compared to TiO2 which had not been sulfate treated. While electrocatalysis using these materials is shown, the discussion of the active site, controlled synthesis, and characterization is the focus of this dissertation.