CAS: IrO2 Based Mixed Metal Oxides for the Selective Oxidation of Methane

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With funding from the Chemical Catalysis program in the Division of Chemistry, Professors Weaver, Hagelin-Weaver and Hibbitts of the University of Florida will study selective methane oxidation using elaborately structured IrO2-based mixed metal oxides. Developing efficient catalytic processes to transform methane, the primary component of shale and natural gas, to more valuable products is a grand challenge for the chemical industry and would have significant economic and environmental benefits. The availability of new and cost-effective methane-to-chemicals processes could incentivize the use of shale and natural gas as a chemical feedstock rather than a combustion fuel, thereby mitigating greenhouse gas emissions and facilitating a transition toward renewable energy. Currently, direct catalytic processes to convert methane to chemicals are scarce and unsuitable for commercial use. The major difficulty is that most catalytic materials must operate at high temperatures to initiate chemical conversions of methane, whereas milder conditions are needed to direct the subsequent chemistry toward desirable products. In this project, the investigators will develop a fundamental understanding of the selective conversions of methane to more valuable chemicals using well-defined oxide catalysts. Designing the catalyst structures with atomic-level precision is necessary for efficiently and selectively converting methane to chemicals. The investigators will provide opportunities for high school and undergraduate students to participate in their research, and focus on recruiting students from underrepresented groups to engage in these activities. These outreach activities seek to promote the science, technology, engineering and math (STEM) disciplines. This project seeks to develop a fundamental understanding of how the local structure and composition of IrO2-based mixed metal oxides influence the oxidation chemistry of methane, and may be tailored to promote the selective oxidation of methane to value-added products, such as ethylene, formaldehyde or other organic oxygenates. The key idea is that atomically dispersed IrO2-sites in a less reactive oxide will induce initial methane activation at low temperature and that subsequent conversion to products will be mediated by the second, more chemically selective oxide. This research involves investigations of the structural and chemical properties of IrO2-modified TiO2 and RuO2 prepared as planar crystalline surfaces as well as nanocrystalline powders. Two general structural motifs are being investigated, namely, Ir atoms substituted into the surface lattice of the host oxide and nanoscopic IrO2 islands dispersed on the host oxide surface. These materials will be investigated using a combination of experimental and theoretical methods including ultrahigh vacuum surface science and catalyst characterization, reactor studies and density functional theory and kinetic Monte Carlo modeling. Key aims of the project are to systematically characterize the atomic-level structures of mixed metal-oxide surfaces of varying composition and morphology and determine how the methane oxidation chemistry is influenced by the local Ir-O structures. The project involves stringent comparisons of the results of first-principles modeling with experimental results obtained from planar crystalline surfaces and more complex nanoparticles to develop a robust understanding of the selective oxidation of methane on the mixed metal-oxides.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.