Collaborative Research: Structure, Dynamics, and Catalysis with Dilute Bimetallic and Single Atom Alloy Nanoparticles

About This Grant

With support from the Chemical Catalysis program in the Division of Chemistry, David Flaherty (Georgia Institute of Technology), David HIbbitts (University of Florida), and Ayman Karim (Virginia Polytechnical Institute) will examine the connections among the structure, dynamics, and catalysis of reactions with oxygen on bimetallic nanoparticles. The team will create, characterize, simulate, and test how atoms of distinct metals move and facilitate reactions upon the surfaces of nanoparticles comprised primarily of gold with small amounts (1-5%) of a second element such as palladium or platinum. These materials are commonly described as single atom alloy (SAA) catalysts. These materials offer high rates and selectivities for numerous reactions important for domestic production of energy carriers and platform chemicals (e.g., valorization of biomass, shale gas, operation of fuel cells and electrolyzers). SAA currently suffer from a distressingly low number of active sites per gram of precious metal used. The collaborative team aims to develop methods to create SAA nanoparticles with smaller diameters (< 2 nm) to remedy this problem, and then test if the emergent and beneficial catalytic properties of these SAA are preserved as the size of the nanoparticles decreases. Here, the team will combine cutting-edge methods in quantum chemical simulations and multiscale modeling, characterization of operating catalysts using synchrotron methods, and catalyst testing and spectroscopy to learn how the nanoparticles restructure in different combinations of reactive gases relevant for catalysis (e.g., oxygen, hydrogen, carbon monoxide). Subsequently, the team will assess how rates and selectivities for a testbed reaction (reduction of oxygen with hydrogen) depend on the spatial organization of the atoms on the nanoparticle surface. Methods that will be developed will be useful for other dynamic catalyst systems and will be integrated into graduate-level courses. The proposed work involves lab-based education of graduate and undergraduate students and focused efforts to increase participation of women in catalysis science, especially with NSF REU (Research Experiences for Undergraduates) opportunities and cross-training of researchers across the three partnering institutions. Under this award, the collaborative Flaherty/Hibbitts/Karim team aims to learn how the structure, dynamics, and catalytic properties of bimetallic and SAA materials depend upon mean particle diameters, composition, and support identity, all factors that impact the coordinative saturation of surface atoms and the identity of their nearest and next-nearest neighbor atoms. The team will couple precise synthesis, advanced characterization techniques (including n situ, operando X-ray absorption spectroscopy, microcalorimetry, infrared spectroscopy), and computational methods (simulations of full nanoparticles with density functional theory and kinetic Monte Carlo) to address the complexity and dynamics of SAA catalysts. A testbed reaction system with rates and selectivities proven to be structure-sensitive with respect to these materials (H2 + O2 → H2O2) will be used to probe the surface structures of active catalysts, a challenge as the high pressures and complex solvents used often render characterization difficult. First, Au-rich bimetallic alloy nanoparticles (i.e., M1Aux materials, where M = Pd, Pt, Rh) with mean diameters of 1-2, ~6 and ~10 nm will be created, their post-synthesis structures will be characterized, and then the influence of adsorption and reactions on their structures will be examined over extended periods. Second, the thermodynamic relationships among adsorption energies, active site motifs, and nanoparticle structure will be determined. Third, the fundamental connections surrounding elemental identity, mole fraction, and coordination of the reactive metal and reaction rates, selectivities and barriers for H2O2 and H2O formation will be examined. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.