Rational Design of Colloidal Noble Metallic and Bimetallic Nanocatalysts and Development of a Microfluidic Reactor Platform for Fundamental Assessment of Catalytic Activity

Multi-phase catalytic hydrogenations play a significant role in converting bio-derived materials to commodity chemicals and liquid fuels. It is desirable to conduct the reaction efficiently, economically and in an environmentally-friendly manner to achieve the goals of green chemistry. However, mass transfer limitations and harsh reaction conditions often interfere with the assessment of intrinsic catalyst performance, and induce undesired side reactions. To provide a partial solution to this problem, we have combined colloid science, nanotechnology, and microfluidics to construct a reaction platform that operates under mild reaction conditions, enables rapid and accurate catalyst assessment, and minimizes or significantly reduces mass transfer limitations. In the first part of this dissertation, we report on the rational design of colloidal noble metallic nanocatalysts, to take advantage of their high surface area to volume ratios and the resulting enhanced surface reactivity. We have used thermal decomposition to synthesize uniform stable noble metallic (palladium, platinum and ruthenium) nanoparticles (NPs) less than 10 nm in diameter. The synthesis procedure was further enhanced by polyol reduction, to improve the yield and efficiency of the process. To better understand the mechanisms of particle formation and to study the effect of size on catalytic properties, we synthesized size-tunable ruthenium (Ru) NPs (3.5 to 130.0 nm) stabilized with poly(vinyl)pyrrolidone (PVP), by systematic manipulation of a number of polyol reduction parameters. Precursor type, reduction temperature and amount of presynthesized particles (foreign seed) added were all found to have significant impact on particle morphology. To investigate the effects of metal composition, we also synthesized palladium and ruthenium (Pd-Ru) bimetallic alloy NPs by co-polyol reduction. Electron microscopy characterization and elemental analysis results confirmed uniform particle morphology and homogeneous composition, and provided information on specific crystal structure. In the second part of this dissertation, we developed continuous flow microreactor systems with metal NPs immobilized on the walls, for fast catalyst screening and performance assessment under minimized mass transfer limitations. The first-generation microreactor was a polydimethylsiloxane (PDMS) microfluidic system fabricated by soft lithography, with NPs synthesized by thermal decomposition and immobilized in-situ. The effectiveness of immobilization in the microfluidic reactors was confirmed by hydrogenation of 6-bromo-1-hexene at room temperature and one atmosphere of hydrogen pressure. The turnover frequencies (TOF) measured in the microreactor were hundreds of times larger than those measured under identical reaction conditions in batch systems. To improve catalyst stability and system compatibility, we developed secondgeneration microreactors using glass capillaries with NPs immobilized on the walls, and used the hydrogenation of cinnamaldehyde to assess catalyst activity and selectivity under different reaction conditions. We also investigated the effects of size and composition on catalyst performance. In summary, the combination of well-defined nanocatalysts and microfluidics significantly enhance the diffusion of hydrogen to catalytic sites, thus eliminating mass transfer limitations and enabling evaluation of the intrinsic catalytic activity. The system provides a convenient platform for high throughput screening of catalysts, and for conducting mechanistic studies of reaction kinetics. Persons with disabilities have the right to request and receive reasonable accommodation. Please call the Department of Chemical Engineering and Materials Science at 355-5135 at least one day prior to the seminar; requests received after this date will be met when possible.