Structural and electronic investigations into subnanometre metallic clusters

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Abdulhussein, Heider A (2019). Structural and electronic investigations into subnanometre metallic clusters. University of Birmingham. Ph.D.

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Abstract

This thesis presents computational studies of the geometric and electronic structures and energetic properties of homo- and heterometallic subnanometre clusters (SNCs). The first two chapters give an introductory overview of nanoparticles and the basics of the sophisticated search algorithms, Genetic Algorithms (GAs), as applied to clusters, and outline a general introduction to the computational methodologies applied in this work, the coupling of the recently developed combination of GAs with Density Functional Theory (DFT) calculations. This is followed by four results chapters, in which these computational methods are adapted to several SNC systems to elucidate their applicability in catalysis. Six publications are documented in the results chapters. Gold-palladium SNCs, which are promising catalysts for a wide variety of chemical reactions, are studied extensively in chapters 3 and 4. Chapter 3 considers the evolution of structural motifs as a function of size and composition for neutral Au-Pd clusters in the gas-phase and supported on a MgO(100) surface. Quantum-regime effects are observed and energetics are further studied. In chapter 4, a rigorous approach is presented to explore structure and stability of mono-cationic Pd-doped Au clusters and their reactivity with CO gas. The Birmingham Parallel Genetic Algorithm BPGA-DFT approach is combined with experimental techniques, including mass spectrometry, and infra-red multiphoton dissociation spectroscopy. This study gives unique insights into Pd dopant effects on cluster stability, as measured by their photo-fragmentation properties, and on their CO adsorption properties. Computational investigations into AuCu SNCs, using the Mexican Enhanced Genetic Algorithm MEGA-DFT code to rationalize the efficient catalytic properties, are presented in chapter 5. Free clusters and those supported on a MgO(100) surface are compared in this approach. The interactions with the support are extensively probed in order to better understand their role in catalysis at the atomistic level. Chapter 6 is dedicated to the structural characterisation, which is vital first step in order to understanding catalytic activity, of Ru-Pt clusters, which are electrode catalysts in direct methanol fuel cells. Ru@Pt core-shell chemical ordering is predicted. Finally, overall conclusions and outlook are presented in chapter 7.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):