Characterization and Optimization of Multifunctional Automotive Catalysts
Malamis, Sotirios A.
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Multifunctional automotive catalysts provide new opportunities for gasoline and diesel engines to meet the constantly tightening emissions and fuel economy standards from various regulatory agencies. Meeting these demands is important not only for securing industrial compliance but also for improving human health and air quality. Combining multiple functions into a single catalyst saves design space and reduces material cost. Here we conduct steady state and transient experiments on multifunctional catalysts that span the operational range of gasoline and diesel engines including cold start and high-temperature operations in order to reduce NOx and hydrocarbon (HC) emissions. We investigate first the Three-Way NOx Storage Catalyst (TWNSC), a concept that combines three-way and NOx storage functionalities for optimal performance during high-temperature vehicle operation. A series of experiments identifies operating conditions that maximize conversion and performance for application with a downstream selective catalytic reduction (SCR) catalyst. Second, we characterize new catalysts that address the cold start issue of modern engines, namely the Lean Hydrocarbon NOx Trap (LHCNT) concept. The LHCNT is a precious group metal (PGM)-zeolite material that combines low temperature NOx and hydrocarbon storage and catalytic conversion of both species into a single unit. By conducting transient uptake and release experiments we obtain useful insight about competitive adsorption, release temperature, conversion activity, and water impact. We find that hydrocarbon concentration and identity, as well as PGM content and zeolite geometry can affect NOx/HC uptake and release performance. Findings from single catalyst function experiments are used to evaluate sequential and dual-layered configurations that improve the overall LHCNT performance. The final part of this work investigates the feasibility of modeling such a catalyst to predict performance and screen new materials. These results provide guidance for improving catalytic systems in the automotive catalysis industry in order to keep up with emission standards.