Collaborative Research: Highly Selective Photocatalysis on TiO2 with Atomically Dispersed Active Centers

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Catalysts accelerate chemical reactions toward preferred products with significant savings in energy and capital costs. Photocatalysts - those that rely on the sun's energy - offer a path to sustainable manufacturing of fuels and chemicals, and also facilitate remediation of environmental pollutants. The project will investigate novel photocatalyst designs for upgrading natural gas to higher-value products and clean-up of nitric oxide from air pollutants. The research will be supplemented by a broad range of educational and outreach activities aimed primarily at K-12 and undergraduate students from underrepresented backgrounds.The project enlists the expertise of three investigators with skills in catalyst synthesis, spectroscopic characterization techniques, and computational catalysis to prepare and characterize structurally well-defined and atomically-dispersed active sites on heterogeneous catalysts. The catalysts will be evaluated for their ability to control the product selectivity of photo-driven reactions and to elucidate the corresponding reaction mechanisms. This project responds to a critical challenge in heterogeneous catalysis that traditional synthesis methods often lead to a variety of catalytic sites that are structurally poorly defined. This diversity of active sites leads to poor reaction selectivity and hinders elucidation of reaction mechanisms. The researchers will address these challenges by synthesizing atomically-dispersed active centers, mononuclear metal sites and surface oxygen vacancies, on titanium dioxide, a prototypical photocatalyst. The project focuses on two technologically important reactions, the oxidation of methane to methanol and the reduction of NO to dinitrogen. The effort involves characterization of the catalysts with advanced techniques, such as HAADF-STEM and EXAFS. Operando infrared, Raman, and X-ray spectroscopies will be employed to provide insights into the mechanism of the surface reactions. DFT calculations will further complement the mechanistic information. The project is expected to generate novel insights into the factors that govern the reaction selectivity of heterogeneous catalytic reactions. The team will pursue a multi-pronged approach to engage underrepresented minorities in this research at their respective institutions and to educate the general public about photocatalysis. Specific activities include participation in the NSF-sponsored Research Experience for Undergraduates (REU) Program, an innovative course for freshmen undergraduate students whose primary declarations are not in the sciences, engagement in outreach activities with local high schools, and a collaborative effort with high-school teachers to introduce students to molecular modeling.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.