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CLEERS Teleconference: Mike Harold, University of Houston
July 23 @ 11:00 - 12:00 EDT
Pt Catalyzed NH3 Oxidation: From Nitric Acid to Diesel Emission Control
University of Houston
Ammonia (NH3) is an important molecule with conflicting roles. On the one hand, NH3 is a commodity chemical; its manufacture is integral to the production of fertilizers and polyamides. The oxidation of NH3 on Pt to NOx (x = 1, 2) is one of the oldest commercialized catalytic reactions; it is the basis for the Ostwald Process for the manufacture of nitric acid. On the other hand, NH3 has emerged as an important reagent in emission control. For the first generation of catalytic converters, NH3 was an inconvenient byproduct and converter design changes were made to minimize its production. For the modern diesel vehicle, NH3 is the NOx reductant of choice. However, due to NH3 toxicity, the NOx reduction must be accomplished without releasing NH3to the environment by Pt-catalyzed NH3 oxidation. While the Ostwald process relies on a high NOx yield, the diesel emission control application requires a high N2 yield.
In this talk we will describe our research in the understanding and design of the structured ammonia slip catalyst (ASC), wherein an NH3 oxidation function is combined with a selective catalytic reduction (SCR) function. We show that a combination of targeted experiments and modeling enable convergence to an optimal architecture that minimizes the Pt loading We will also describe advances in the understanding and modeling of NH3 oxidation kinetics, linking the environmental and chemical manufacturing applications. Finally, we will present a novel core-shell catalyst that comprises a Pt/Al2O3 core and a SCR shell provide for unparalleled ammonia oxidation activity and N2 selectivity.