Ellis Hammond-Pereira Passed His Preliminary Exam!

Congratulations to Ellis for passing his preliminary exam today!

Abstract

Nanoparticle catalysts have marked a new age for heterogeneous catalytic research. Materials previously thought inert are suddenly at the cutting edge of modern studies; more complex catalyst structures are constantly drafted and studied. Supported, functionalized, multimetallic heterogeneous catalysts are able to achieve impressive performance by mixing several forms of chemical and physical interactions. As the average nanocatalyst complexity increases, so too does the difficulty fundamentally understanding the chemistry responsible for their impressive performance. Without such fundamental knowledge, the field will remain predominantly driven by unguided experimentation, inevitably falling out of favor as prohibitively complex systems are required for a chance at a breakthrough. While research that pushes the boundaries and brings new ideas is important, there is an inarguable need to more deeply analyze the reason for these discoveries in the first place. The long-term goal of this proposal is to provide a set of criteria for catalyst improvement based on fundamental catalyst properties and the impact of modification on said properties. The central hypothesis is both silica functionalization and pore size of silicaencapsulated gold (Au@SiO2) core-shell nanoparticles predictably impact gold surface chemistry and
diffusion of reactant in ways that measurably influence the catalysis of aerobic benzyl alcohol oxidation. The first aim is to determine the effect of pore size and ligand electronegativity on catalyst surface charge of Au@SiO2 core-shell nanoparticles. It is hypothesized that increasingly electronegative ligands will interact with the gold surface, inducing a positive charge. This positive charge will be measureable via xray photoelectron spectroscopy (XPS) as either a positive shift in binding energy or the appearance of higher gold oxidation states depending on the strength of interaction. The second aim is to determine the impact of pore size and functionalization on mass transport through the porous silica. It is hypothesized that ligand hydrophobicity can either help or hinder diffusion through the pores depending on pore size. In larger pores hydrophobic ligands can encourage movement towards the gold surface by reducing
reactant interaction with the pore wall. In smaller pores the hydrophobic environment can become so overwhelming as to completely discourage entry into the pores. Diffusion order spectroscopy nuclear magnetic resonance (DOSY NMR) will be used to measure the diffusion coefficient of reactants within the catalyst pores. The third aim is to synthesize and demonstrate performance of an optimized catalyst, linking surface chemistry and mass transport to traditional measures of catalytic performance. Using the results from the first two aims, the nanoparticles will be used to catalyze aerobic benzyl alcohol oxidation. The catalytic performance will be compared using turnover frequency, selectivity towards benzaldehyde,
and catalyzed activation energy. In aggregate, the research will be impactful for the nanoparticle catalysis field by providing an actionable roadmap for catalyst tuning and design, reducing the elements of randomness associated with functionalized nanoparticle design.