Engineering Nanostructured Inorganic Materials and Nanoscale Stabilized Structural Features for Heterogeneous Catalysts
Open Access
- Author:
- Darling, Albert
- Graduate Program:
- Chemistry
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 14, 2021
- Committee Members:
- Benjamin Lear, Major Field Member
Robert Rioux, Outside Unit & Field Member
Elizabeth Elacqua, Major Field Member
Raymond Schaak, Chair & Dissertation Advisor
Philip Bevilacqua, Program Head/Chair - Keywords:
- Nanomaterials
Hydrogen Evolution Reaction
Nitroarene Hydrogenation
Catalysis
High Entropy Alloys
Bulk-Immiscible Alloys
Heterogeneous Catalysis - Abstract:
- Nanomaterials have long stood as excellent platforms for achieving efficient catalytic performance, owing to their intrinsic high surface area to volume ratio. In addition, nanoscaling has demonstrated promise in the stabilization of structural features, such a novel phases or surface defects, which can significantly alter the catalytic properties of their respective materials. In this dissertation, I build on these foundations through the development of new catalytic materials for both the selective hydrogenation of nitroarenes and the hydrogen evolution reaction. With these advances, I leverage nanoscale-stabilized structural features as well as nanostructuring to develop high-surface area catalysts that exhibit intrinsically high catalytic performances, offering insights into how the structural motifs observed with these materials underpin their excellent catalytic properties. These insights will be instrumental for the development of next-generation nanomaterials for sustainable catalysis. In a collaboration with Dr. Yifan Sun, I begin by demonstrating colloidally synthesized WS2 few-layer nanosheets as an active and selective catalyst for the hydrogenation of substituted nitroarene molecules. Owing to nanoscale stabilization effects, these 2D materials exhibit a much higher concentration of surface defects than bulk transition metal dichalcogenides, which exhibit no activity for these catalytic transformations. Collaborative computational studies reveal the sulfur defects and tungsten-terminated edge sites on these nanomaterials are responsible for the activity and selectivity they exhibit for nitroarene hydrogenations. Given that mechanistic insights into the origins of selectivity for these transformations remain rare for non-platinum-group catalysts, these results will be instrumental for the future rational design of sustainable materials for selective organic transformations. Next, I demonstrate both surface-roughened Ru4Al13 bulk crystals (studied in collaboration with Kriti Seth) and classically immiscible ligand-free AgRh alloy nanoparticles as high-performing, acid-stable catalysts for the hydrogen evolution reaction. These studies present two different methods of nanostructuring to achieve high surface area catalytic materials: surface dealloying of bulk crystals and the bottom-up colloidal synthesis of nanoparticles. The high performance of the bulk Ru4Al13 crystals can be attributed to the in-situ formation of a Ru-rich surface that features high-surface area pits and trenches derived from the Al dealloying process. This surface-nanostructuring methodology is potentially generalizable for the future engineering of high surface area crystals of materials for which the direct synthesis of nanoparticles remains a challenge. In contrast, the excellent catalytic properties of the AgRh nanoparticles, which inherently have a high surface area, is derived from synergistic effects between the two alloyed metals. These results represent the first reported utilization of solution-synthesized alloys of metals that are classically immiscible (i.e. stable only on the nanoscale) as a catalyst for electrocatalytic hydrogen evolution, suggesting that this class of materials may be a rich phase space with which sustainable production of hydrogen can be achieved. Finally, I expand my work to high entropy materials, demonstrating the first reported method by which non-noble metals may be incorporated into complex solid solution nanomaterials through one-pot colloidal methods. Homogeneous CuIrPdPtRh and NiIrPdPtRh alloy nanoparticles are synthesized via the hot injection of metal salt precursors into a solution of high boiling point solvents and surfactants. Control studies reveal that the slow injection rates followed by rapid quenching are key for the formation of a single alloy phase. In addition, I demonstrate that this synthetic method may be useful for incorporating high entropy alloy phases into complex heterostructures through preliminary evidence for core-shell particle formation. These advances will be important not only for the future development of tailor-made complex heterostructures, but also for the design of tunable nanomaterials for multi-step catalytic reactions.