This dissertation contains two parts. The first part describes a transformational synthetic methodology for precious metal nanocatalysts. Current synthesis route of precious metal nanoparticles typically adopts a so-called “bottom-up” approach, in which metal ions or their ligand molecules are used as building blocks to assemble the corresponding nanoparticles. However, this current state-of-the-art methodology also introduces various limitations and complications, such as the complicated preparation of precursors, the harsh requirements on the stability and surface charge of the support materials, and the reduction potential of different metals etc.
Through reverse-thinking methodology, the so-called “top-down” strategy for nanomaterials synthesis is adopted. This strategy is exactly opposite to the conventional “bottom-up” approach, in which bulk precious metals or their alloys are used as starting materials to directly disperse them into small nanoparticles in liquid lithium. The phase diagrams of precious metals in lithium suggest that nearly all precious metals can be dissolved in liquid lithium at moderate temperatures.
As a proof-of-concept, supported platinum nanoparticles are prepared from Li-Pt solid solution. The lithium is converted to LiOH, which is further mixed with carbon black as support material. The lithium content in the mixture can be selectively leached off by water so that Pt nanoparticles can be transferred to any nonaqueous support materials. The nanoparticles are characterized by various techniques including TEM, SEM-EDX, and EXAFS. The catalytic properties of the synthesized nanocatalysts are also studied in clean energy systems such as the catalysts for oxygen reduction reaction in hydrogen fuel-cells.
This method is also utilized to uniformly dope catalytic palladium nanoparticles in a potential hydrogen storage material, Li3N. Without a support, nanoclusters of Pd are distributed in Li3N. The potential application of this method for chemical hydrogen storage materials is shown by the enhanced hydriding kinetics at moderate temperatures.
This top-down synthetic strategy for precious metal nanoparticles is extended for the synthesis of bimetallic precious metal nanoparticles. As an example, Pd3Ag alloy nanoparticles are prepared by directly dispersing the bulk Pd3Ag alloy in liquid lithium. The obtained Pd3Ag nanoparticles are extensively characterized by XRD, TEM, EXAFS, XANES, and CV. The prepared Pd3Ag alloy nanoparticles exhibit oxidation-inert property at room temperature.
The new synthetic methodology developed in this dissertation opens a new door for the synthesis of alloy nanoparticles that are very difficult if not impossible to be obtained using the conventional precursor-based method (the “bottom-up” approach).
In the second part of this dissertation, a novel in situ electrical study of the effect of hydrogen spillover, on carbon support is discussed. It is found that the conductance of a percolating Pd nanoparticle layer on amorphous carbon reflects the mechanism of primary hydrogen spillover. This effort provides a simple alternative way for in situ study of catalytic effect.
|Commitee:||Gaillard, Elizabeth R., Hosmane, Narayan S., Sunderlin, Lee S., Zheng, Chong|
|School:||Northern Illinois University|
|Department:||Chemistry and Biochemistry|
|School Location:||United States -- Illinois|
|Source:||DAI-B 72/12, Dissertation Abstracts International|
|Subjects:||Chemical engineering, Nanotechnology, Materials science|
|Keywords:||Bimetallic nanoparticles, In situ electric study, Nanoparticle synthesis, Precious metal catalysts|
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