Defect Chemistry of Metal Oxides for Catalytic Reactive Oxygen Species Generation

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With this award, the Chemical Catalysis Program is funding Chin Li Cheung of the University of Nebraska at Lincoln and Wai-Ning Mei of the University of Nebraska at Omaha for research to investigate how certain industrially important catalysts function. The specific focus of this project seeks to understand how defects in tiny metal oxide particles lead to their ability to function as catalysts. One of oxides being studied, a substance known as cerium oxide, is used extensively as a catalyst in automobile catalytic converters, as a key component in petroleum refining, and in a wide variety of chemical manufacturing applications. Despite its widespread use and importance to industry, the mechanism for cerium oxide's catalytic activity is still not well understood. To investigate this in more detail, the group is preparing small particles of cerium oxide with imperfections, or defects, on their surfaces. These small particles are also being prepared in such a way that they contain foreign metals, or dopants, also thought to be related to their catalytic activity. The ability of these carefully prepared particles to catalyze chemical reactions is determined and, then, correlated with the defects and dopants that are present. The group is using computer modeling to more fully understand the reactions that may be taking place during catalysis. With this combined experimental and theoretical approach, the investigators are able to more completely control the catalytic activity of these small particles and more fully understand how they function. The work is having a broad impact on industry and technology, and may lead to improved catalysts for a wide variety of technological applications. The work is having a further broad impact through the engagement of students at both the undergraduate and high school level. Even younger students are being included in the work through an innovative summer camp program for middle school and home-schooled students. This project aims to develop a fundamental understanding of the role of surface-subsurface defect interactions on the chemical activity of surface binding sites that are involved in molecular adsorption in metal oxide systems of reduced dimension. Such knowledge is expected to yield catalytic pathways for reactive oxygen species (ROS) generation and annihilation with reducible metal oxide in the environment and in industrial processes. Ceria nanoparticles with different shapes, facets and chemical impurity content are being synthesized by hydrothermal methods. The kinetics of the catalytic reactions of these particles with hydrogen peroxide to generate ROS are being determined. Analysis of the kinetic data coupled with DFT modeling are used to identify the effect of subsurface defects on the molecular adsorption energies at the surface binding sites and to determine potential molecular reaction pathways.