UC Berkeley

Abstract

Metal-Semiconductor Hybrids and Pt-Ga Alloys for Catalytic Applications

by

Fadekemi Adetola Oba

Doctor of Philosophy in Chemistry

University of California, Berkeley

Professor A. Paul Alivisatos, Chair

Catalyst design using nanocrystals unlocks a wealth of independently tunable parameters which can optimize the catalytic performance of a material. The controlled placement of nanocrystals with distinct size, shape and composition within a single particle combines the advantages of each individual component for targeted reactions. Furthermore, the tailored mixing of two or more elements within a single nanocrystal can lead to novel properties distinct from the single elements themselves. Such parameters can be useful in enhancing the activity, selectivity and stability of a catalyst under reaction conditions. Thus, special attention must be paid to the assembly of such catalysts. Solution phase synthesis is a versatile tool for creating complex nano-architectures in a rational and controlled manner.

Catalytic reactions often have competing unwanted side reactions which lead to deactivation or degradation. Nanocrystal building blocks can be tuned to address these issues on an atomic level. Furthermore, structure-activity relationships can elucidate information regarding the nature of the active site when the catalyst itself has been carefully designed, assembled and thoroughly characterized. This dissertation covers the colloidal synthesis of platinum and ruthenium loaded chalcogenide semiconductor nanocrystals for applications in water splitting, as well as platinum-gallium alloy nanocrystals for propane dehydrogenation.

Chapter 1 of this dissertation reviews the fundamentals of semiconductor nanocrystals, which covers the basic properties of nanocrystals, background on their colloidal synthesis and requirements to achieving solar water splitting. The design of a platinum and ruthenium loaded core/shell cadmium selenide/cadmium sulfide nanorod is introduced. Chapter 2 discusses the synthesis of this four component heterostructure, detailing crucial considerations that must be addressed when assembling such multicomponent structures. Initial photocatalytic studies are presented at the end, followed by synthetic approaches to replacing ruthenium with iron or cobalt oxide based materials. Chapter 3 reviews some fundamentals of metal nanocrystals and the synthesis/applications of alloys in heterogeneous catalysis. A brief background on propane dehydrogenation is provided, with a succinct description of major problems encountered and proposed solutions. This precedes the synthetic development and characterization of platinum-gallium nanocrystals for propane dehydrogenation in Chapter 4. Chapter 5 presents the in-situ monitoring of structural changes which occur under experimentally relevant conditions and initial propane dehydrogenation studies. Concluding remarks are summarized in Chapter 6, followed by an appendix of additional results and references.