Pd/Zeolite Passive HC/NOx Adsorbers
Mark Crocker, University of Kentucky
Trevor Lardinois1, Jason Bates1, Rajamani Gounder1, Robert B. Pace2,3, Yaying Ji2, Mark Crocker2,3, Jeroen Van der Mynsbrugge4, Alexis Bell4
1Charles D. Davidson School of Chemical Engineering, Purdue University
2University of Kentucky Center for Applied Energy Research
3Department of Chemistry, University of Kentucky
4Department of Chemical and Biomolecular Engineering, University of California, Berkeley
Standard automotive aftertreatment technologies fail to function efficiently at low temperatures, from which it follows that high efficiency internal combustion engines require new and/or improved technologies which specifically address their low exhaust temperatures. This is made imperative by the implementation of U.S. Tier 3 legislation, which will require that both NOx and hydrocarbons (HC) are effectively controlled during cold starts. Against this backdrop passive HC/NOx adsorbers represent a promising technology, since they present a means to mitigate both HC and NOx emissions at temperatures down to ambient. However, fundamental understanding of the chemistry of NO/HC adsorption and reaction in Pd/zeolites is currently lacking. Moreover, data pertaining to the stability of these catalysts under typical gasoline and diesel conditions has yet to be published, and the mechanisms underlying their degradation during aging are yet to be elucidated. In this presentation we will report initial results from work designed to address these issues.
Our approach employs Pd/H-BEA and Pd/H-CHA adsorbers. Pd/H-CHA is an ideal system for study, given its relative simplicity. Indeed, while there are nine discrete framework aluminum sites (and thus the same number of ion-exchange sites) in BEA, there is only one such aluminum site in CHA, rendering CHA more amenable to theoretical modeling studies. In parallel, we are conducting the same experimental and computational investigations using Pd/H-BEA, given that it possesses superior low temperature (≤ 100 °C) NO storage capacity compared to Pd/H-CHA and Pd/H-MFI .
Initial work has involved the synthesis of Pd/H-CHA and Pd/H-BEA catalysts, followed by their extensive characterization using a range of physico-chemical methods. Subsequent catalyst evaluation has been based on temperature-programed adsorption/desorption methods and kinetic measurements, as well as in situ spectroscopic measurements to probe the nature of the Pd species present and their evolution with sample treatment (e.g., exposure to oxidizing and reducing conditions). In parallel, NO/HC adsorption and related reaction pathways are being studied by means of quantum chemical calculations in order to rationalize the experimental data and provide additional insights.
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