NSF-DFG Confine: Plasma-Catalysis in Confined Spaces for Cold Start NOx Abatement in Automotive Exhaust

This project seeks to transform traditional chemical processing to ensure a sustainable future. Catalysis, which facilitates desired chemical reactions, has played a key role in defining the modern standard of pollution abatement, high-energy density fuels, and proficient and safe fuels and fertilizers. This project aims to develop an understanding of new concepts in the practice of chemical catalysis enabled by coupling of non-equilibrium plasma with surface catalyzed reactions. NOx abatement in capillary microreactors, mimicking “honeycomb monoliths” in modern-day catalytic converters, at near ambient temperatures serve as a testbed system. Tailpipe emissions in transportation account for a majority of NOx pollution harming human health and the environment. State-of-the-art automobile exhaust after-treatment systems remediate NOx efficiently above a threshold light-off temperature >473 K (>200 degrees C), sufficient to overcome kinetic limitations inherent in catalytic processes. The project harnesses interactions among plasma chemistry and thermocatalytic processes in confined geometries to enable NOx reduction in automobiles at near ambient temperatures. This addresses “cold start” automotive emissions during engine warm up, which account for >80% of NOx vehicular pollution. This project furthers US-German scientific collaboration and training in STEM.Plasma chemistry occurs volumetrically and involves short-lived reactive intermediates—ions, radicals, electronically- and vibrationally-excited species—which when impinged on a selective catalytic surface could effect chemical transformations and pathways inaccessible to conventional catalysis. The disparity in reaction timescales of plasma (sub-10^-6 to 10 s) and catalytic chemistry (10^-1 to 10 s) and the different length scales for plasma (volume) and catalytic (surface) chemistry implies that effective coupling between plasma and surface catalytic chemistry can only be achieved if surface-to-volume ratios are large to enable a high flux of short-lived plasma-derived intermediates to the catalyst surface. Hence, confinement, enabling very high surface-to-volume ratios, is key to coupling volumetric and fast plasma chemistry with selective, slower surface-based catalytic processes. The project combines reactor design, advanced spectroscopic and spectrometric diagnostics, and multiscale modeling to examine reaction and transport phenomena impacting plasma-catalytic chemistry coupling in confined reaction environments. This includes (1) probing characteristic diffusion time scales and lifetimes of reactive species in combined operation of plasma- and thermocatalytic processes within capillary microreactors, (2) developing spectroscopic and spectrometric tools to identify and enumerate short-lived reactive intermediates in the gas phase and on catalyst surfaces and (3) developing multiscale models describing the underpinning processes in these confined reaction environments. This will allow to elucidate how reaction and transport phenomena impact plasma-catalytical coupling and describe new catalytic species and pathways for NOx reduction. This project was awarded through the “Chemistry and Transport in Confined Spaces (NSF-DFG Confine)" opportunity, a collaborative solicitation that involves the National Science Foundation and Deutsche Forschungsgemeinschaft (DFG).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.