(314a) Modeling Studies of Trapping and Conversion of NOx and Hydrocarbons in a Structured Catalytic Reactor: Pd/SSZ-13 and Pd/Pt/BEA

Advanced after-treatment technologies like Selective Catalytic Reduction, are successful in addressing NO+NO₂ emissions at temperatures above 250ºC. But, emission control during vehicle cold-start (< 150ºC), remains a major challenge. The Hydrocarbon Trap (HCT) and Passive NO_x Adsorber (PNA) respectively capture HCs and NO_x at low temperatures, with their release at higher temperatures for reduction and oxidation conversion. The combination of HCT and PNA poses a number of questions about materials selection, adsorption-reaction-transport coupling, and operating strategy to achieve emission targets. The objective of this study is to develop a model to understand the transient coupling and to converge on the best configurations for combined NO_x and HC trapping, release, and conversion.

A one-dimensional two-phase transient monolith model containing a mechanistic-based microkinetic scheme is developed to explain the NO_x uptake and release over Pd/SSZ-13 with and without CO, C₂H₄, and C₁₂H₂₆ in the feed. A combination of DRIFTS, DFT calculations, and literature data were utilized to develop and tune a microkinetic model for the PNA monolith¹. The model involves Z^-[PdOH]⁺, Z^-Pd⁺, and Z^-Pd²⁺Z^- as NO adsorption sites. The tuned model predicts the NO uptake and NO + NO₂ release over a wide range of conditions and in the presence of exhaust components CO and C₂H₄. The model was validated at different uptake temperatures, temperature programmed desorption (TPD) ramp rate, and feed flow rates, affording its use to validate the experimental findings. Selected modeling results are shown in Fig. 1. Work is ongoing to combine NO and HC trapping and oxidation² to evaluate coupled NO and HC trapping in various PNA + HCT/OC configurations.

Literature Cited

1. M. Ambast, K. Karinshak, B. M. M. Rahman, L. C. Grabow, M. P. Harold, Appl. Catal. B, in press, 2020.
2. P. Y. Peng, M. P. Harold, D. Luss, Chemical Engineering Journal 355 (2019) 661–670.