Chemistry & Biochemistry Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2752
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Item Earth Abundant Bimetallic Nanoparticles for Heterogeneous Catalysis(2014) Senn Jr, Jonathan Fitzgerald; Eichhorn, Bryan; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Polymer exchange membrane fuel cells have the potential to replace current fossil fuel-based technologies in terms of emissions and efficiency, but CO contamination of H2 fuel, which is derived from steam methane reforming, leads to system inefficiency or failure. Solutions currently under development are bimetallic nanoparticles comprised of earth-abundant metals in different architectures to reduce the concentration of CO by PROX during fuel cell operation. Chapter One introduces the Pt-Sn and Co-Ni bimetallic nanoparticle systems, and the intermetallic and core-shell architectures of interest for catalytic evaluation. Application, theory, and studies associated with the efficacy of these nanoparticles are briefly reviewed. Chapter Two describes the concepts of the synthetic and characterization methods used in this work. Chapter Three presents the synthetic, characterization, and catalytic findings of this research. Pt, PtSn, PtSn2, and Pt3Sn nanoparticles have been synthesized and supported on γ-Al2O3. Pt3Sn was shown to be an effective PROX catalyst in various gas feed conditions, such as the gas mixture incorporating 0.1% CO, which displayed a light-off temperatures of ~95°C. Co and Ni monometallic and CoNi bimetallic nanoparticles have been synthesized and characterized, ultimately leading to the development of target Co@Ni core-shell nanoparticles. Proposed studies of catalytic properties of these nanoparticles in preferential oxidation of CO (PROX) reactions will further elucidate the effects of different crystallographic phases, nanoparticle-support interactions, and architecture on catalysis, and provide fundamental understanding of catalysis with nanoparticles composed of earth abundant metals in different architectures.Item Architecturally Controlled Bimetallic Nanoparticles for Heterogeneous Catalysis(2007-03-28) Zhou, Shenghu; Eichhorn, Bryan; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This work develops synthetic methods for architecturally controlled AuPt and CuPt bimetallic nanomaterials. The AuPt heteroaggregate, AuPt alloy spherical nanoparticles, and AuPt alloy nanowires were prepared by a sequential or co-reduction method. The unique AuPt heteroaggregate nanostructures, synthesized by the sequential reduction method, contain Au cores with Pt tendrils extending from the Au surfaces. The AuPt alloy nanoparticles or nanowires were prepared by the rapid co-reduction method. This rapid co-reduction method prevents the phase separation and traps the metastable AuPt alloy phase. The AuPt heteroaggregate, alloy spherical nanoparticles, alloy nanowires, and the reported Au@Pt core-shell structures, constitute the rare example of a bimetallic system containing all reported architectures in the literature. Kinetically stabilized Cu@Pt core-shell nanoparticles were prepared by deposition of Pt onto Cu nanoparticles. The Cu@Pt particles exhibit high stability toward alloying upon annealing. In contrast, the Pt@Cu particles readily transform into alloy structures in the same conditions. This abnormal stability of the Cu@Pt particles is attributed to the Kirkendall mass transport effect, where the inherent diffusion direction from the Pt to Cu is hindered by a limited population of vacancies in the Cu cores. These architecturally controlled bimetallic nanomaterials were applied in CO tolerant hydrogen oxidation and de-NOx reactions with hydrogen. In the H2/CO/O2 fuel, the AuPt alloy nanoparticles are CO tolerant in hydrogen oxidation, and the AuPt heteroaggregate nanoparticles exhibit enhanced preferential CO oxidation in the presence of Fe promoters. In the NO/H2 reaction, the Cu@Pt nanoparticles maintain the high activity of pure Pt particles and have a higher selectivity for N2. Under 4/1 H2/NO conditions, the selectivity for N2 over the Cu@Pt catalyst is 45%. In contrast, under the same conditions, the pure Pt catalyst exhibits a selectivity of 22%. The Pt@Pd catalyst enhances activity as well as selectivity due to the near surface alloy effect.