Understanding the Mechanism of C-X hydrogenolysis Catalyzed by Supported Metal Nanoparticles

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With funding from the Chemical Catalysis Program of the Chemistry Division, Professors Austin of Barnard College, Frederick and Schwartz of University of Maine, and Grabow of University Houston will study how to catalytically reduce off carbon-halogen bonds. The work is of relevance to the chemistry of the environment. In particular, a number of modern pesticides contain such carbon-halogen (iodine, bromine, chlorine, or fluorine) bonds. These molecules have been designed in part because they are stable, but that stability can also becomes a liability at the end of the projected product life cycle. This collaborative team will use a range of approaches to learn how to selectively reductively remove the halogens from these molecules. The team will also study catalysts that can break these bonds to understand precisely how they carry out this important chemistry, and build computational models to design new catalysts of greater practicality. All of the members of the team are committed to diversifying the scientific workforce. The PIs will work to recruit women into science, and into this research team in particular, through a newly formed 4 + 1 program at Barnard College, that provides program participants with the opportunity to complete a master's degree in chemical engineering at Columbia University in just one year after completing their specialized undergraduate degree at Barnard College. The selected students will spend time in a chemical engineering lab at the University of Maine and a computational chemical engineering lab at the University of Houston, in addition to time working at Barnard College and in the materials characterization labs at Columbia University, so that they will learn all of the facets of this multidisciplinary effort.This research project will test several mechanistic hypotheses about the nature of aromatic C-X bond hydrogenolysis catalyzed by supported metal nanoparticles. Reaction rate data for C-X bond hydrogenolysis in aromatic compounds shows a surprising lack of sensitivity to the identity of X, implying that C-X bond breaking is not rate-determining. The team hypothesizes that surface chemistry plays a critical role in dehalogenation of halogenated aromatic compounds in ways that are very different from the chemistry for the analogous alkyl-X species. The collaborative team will study the detailed steps of C-X bond hydrogenolysis on systems of increasing complexity and use data from those studies to inform density functional theory (DFT) calculations and allow for the joint experimental/computational team to build micro-kinetic models.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.