Effective Model of NO x Adsorption and Desorption on PtPd/CeO 2 -ZrO 2 Passive NO x Adsorber
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Effective Model of NOx Adsorption and Desorption on PtPd/CeO2‑ZrO2 Passive NOx Adsorber Anežka Kvasničková1 · Petr Kočí1 · Yaying Ji2 · Mark Crocker2,3 Received: 12 December 2019 / Accepted: 13 March 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract An effective model for describing NOx adsorption and desorption on a PtPd/CeO2-ZrO2 passive NOx adsorber is presented. The kinetic parameters are evaluated from the available experimental data obtained during N Ox adsorption/desorption experiments including CO2 and H 2O in the feed, performed at 80, 120 and 160 °C both in the presence and in the absence Ox adsorption rate and capacof reducing agents (CO or C 2H4 ). The model describes the temperature dependence of the N ity, the impact of CO, and dynamics of the NOx desorption events. The model predicts formation of nitrites, nitrates, and additional storage enabled in the presence of CO. Thermal decomposition of the stored N Ox species results in two main desorption peaks. Nitrites are desorbed at lower temperatures while nitrates are thermally more stable. The evolution of nitrite and nitrate species in the model corresponds with the measured DRIFTS spectra of the catalyst surface. The presence of CO significantly improves the rate of NOx adsorption and storage efficiency at low temperatures, most probably due to reduction of oxidic Pt and Pd nanoparticles. The developed model captures well the observed trends and can be utilized for simulations of PNA performance under real operating conditions. Keywords PNA · Automotive exhaust gas aftertreatment · PtPd/CeO2-ZrO2 catalyst · Mathematical modeling · NOx adsorption
1 Introduction The control of N Ox emissions from lean-burn engines during cold starts is still an on-going issue. Currently, commercially used technologies for NOx abatement are Selective Catalytic Reduction (NH3-SCR) and Lean NOx Trap (LNT, also known as N Ox Storage and Reduction Catalyst, NSRC). However, these methods are unable to reduce NOx efficiently at temperatures below 200 °C [1]. Therefore, the major part of the overall NOx emissions is generated during * Petr Kočí [email protected] Mark Crocker [email protected] 1
Department of Chemical Engineering, University of Chemistry and Technology, Prague, Technická 5, Prague 166 28, Czech Republic
2
Center for Applied Energy Research, University of Kentucky, 40511 Lexington, KY, USA
3
Department of Chemistry, University of Kentucky, 40506 Lexington, KY, USA
the cold start, when the deNOx system has not warmed up to its operating temperature. Since environmental regulations are increasingly restricting the permitted NOx limits, an effective NOx abatement during cold starts will be required. The solution may be represented by the application of a so called passive NOx adsorber (PNA) [2]. The task of the PNA is to temporarily store nitrogen oxides during cold starts and release them when the main N Ox reduction catalyst reaches its operating temperature. PNA techno
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