Our work is focused on the synthesis of noble metal and noble metal alloy nanoparticles with well-defined shapes and catalytically active high-energy surfaces. Our research takes place at the interface between inorganic chemistry and materials science, and we combine solution-phase nanoparticle synthesis with advanced materials characterization techniques such as scanning electron microscopy (SEM). In addition, we evaluate the catalytic activity of new materials using both gas-phase (continuous flow reactor coupled with gas chromatography/mass spectrometry, GC/MS) and solution-phase (electrochemistry) techniques.
The relationship between structure and function is particularly interesting for metal nanoparticles because their physical and chemical properties, including catalytic and optical activity, are highly dependent not only on their material composition, but also on their size and shape. Recent advances in nanoparticle synthesis and characterization have led to an improved ability to produce metal nanoparticles with tailorable sizes, shapes, and compositions. Metal nanoparticle growth is highly sensitive to reaction conditions, and this opens up a broad parameter space in which to design exciting new materials. The mechanisms behind the formation of metal nanoparticles with defined shapes are based on fundamental chemical parameters and concepts such as reduction potential, solubility, binding strength, and reaction kinetics. In our lab, we seek not only to develop syntheses for new, catalytically active materials, but also to understand the complex mechanisms which direct the formation of these novel structures so that we may use these principles to design nanostructures with finely tailored properties. In particular, our current focus is on the synthesis of noble metal nanoparticles with new shapes defined by high-energy surfaces and that have a sub-monolayer coverage of a second metal. These materials have strong potential as catalysts due to the synergistic reactivity that emerges from the interactions between multiple metals as well as the increased activity that results from the atomic steps and kinks which are present in high-energy surfaces.
Energy- and Material-Efficient Catalysis
A majority of current industrial chemical processes rely on a catalyst to increase the rate of reaction. Many of these catalysts are heterogeneous, where the phase of the catalyst (solid, liquid, gas) differs from that of the reagents. Heterogeneous metal catalysts are commonly nanoscale in size because nanomaterials have a high ratio of active surface area to total volume, which ensures efficient use of limited precious metal resources, thus minimizing cost. One key way to improve the sustainability of energy generation and chemical production is through the development of new nanoscale heterogeneous catalysts with enhanced activity and selectivity. In our lab, we take two approaches in addressing this challenge: (1) gas-phase reactions catalyzed by highly-faceted nanoparticles with tailored bimetallic surface compositions, and (2) electrochemical solution-phase reactions using metal nanostructures with well-defined shapes grown on electrodes as catalysts. Our goal is to establish structure-function relationships which guide the design of nanostructured catalysts to enable important chemical transformations that are currently too slow or that have low yields of the desired product. Such reactions include, but are not limited to, the selective partial oxidation of furfural and 5-hydroxymethylfurfural (biomass feedstocks), the oxidation of methanol to generate hydrogen (fuel cells), and the selective hydrogenation of α,β-unsaturated aldehydes (sustainable chemical production).