Marlow, Sushila Marie; (2024) Rate Determination in Metal Nanoparticle Synthesis and Catalysis. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This research explores the role of reaction rates and intermediate species in the synthesis and catalysis of transition metal nanoparticles using high-resolution in situ spectroscopic techniques. Experimental measurement of time-resolved data during a reaction, though challenging, affords fundamental insights into the reaction mechanisms, transient states and nanoparticle behaviour, as a foundation for theoretical calculations. The projects presented advance the measurement and analysis of in situ data, at the limits of time-resolution and elemental-detection. After the introduction (Chapter 1) and scientific background (Chapter 2), Chapters 3 to 7 reveal the rates of synthetic reduction and electrochemical oxidation of Pd, Pt-Pd and Cu nanoparticles, obtained primarily from in situ X-ray absorption spectroscopy. First, a 500 ms-time-resolved study of CTAC-capped Pd nanoparticle growth (Chapter 3), with a series of temperatures and seed solutions, measured the growth profile, activation energy and, for the first time, the formation of soluble Pd(0)-Cl intermediates. Applied in Chapter 4, Pt-Pt coordination number alloyed in a Pd nanoparticle matrix was studied as a descriptor for Oxygen Reduction Reaction activity. Extreme ratio Pt1Pd493 nanoparticles containing Pt dimers, inhibited Pt oxidation and increased atomic efficiency. The role of the surfactant during growth was studied in Chapter 5, where CTABinduced faceted Pd nanoparticle morphology did not significantly form soluble Pd(0)-Br, due to the Pd-ligand interaction and exhibited a different growth profile. A 1.27 ms-resolved study of early-stage Cu nanoparticle formation captured the effect of intermediate Cu1+ species and hydrazine-complexation in determining morphology (Chapter 6). Lastly, the rate of electrochemical oxide-formation at a Cu surface was observed with µs-resolution (Chapter 7), with the aim of enhancing CO2RR activity. The driving principle behind this research is that such detailed experimental measurements of nanoparticle synthesis and catalytic behaviour, is a necessary foundation for the ‘rational design’ of catalysts over more costly and laborious trial-and-error.

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