Global Kinetic Modelling of a Supplier Barium- and Potassium-Containing Lean NO_x Trap

Abstract

Kinetic modeling, in combination with flow reactor experiments, was used in this study to simulate a supplier lean NO x trap (LNT). The LNT catalyst used is a commercial catalyst that contains barium and potassium as storage components. The results presented in this paper are a continuation of a previous study, where a global kinetic model for NO x storage was developed for a model Pt/Rh/BaO/Al2O3 catalyst. In this work, a simplified model is used, where NO oxidation, nitrite, and nitrate formation are lumped together into one reaction, and the model predicts the total NO x . In this model, only one reaction step must be tuned for each storage component: that is, in our case, one reaction for the formation of barium nitrate and one reaction for potassium nitrate. A broad range of experimental conditions was used when developing this model; five temperatures (200, 300, 400, 500, and 600 °C) and three different inlet NO concentrations (100, 200, and 300 ppm) were used. Water and CO2 were present in all experiments, because these can affect the storage behavior. The reductant used in the regeneration period was CO. Long lean and rich cycles were used to capture the kinetics of the reactions accurately. The model was able to describe all 15 experiments well and could adequately capture the amount of stored NO x during the lean period and the NO x conversion during the rich period, including the NO x breakthrough peak that occurred at the beginning of the rich period. The model was validated with short lean−rich cycling experiments, where the lean period was 30 s and the rich period was 2 s. The model could predict the outlet NO x concentration well, and the error for the average conversion was only 1%−2% in the validation simulations.

Flame-Made Pt/K/Al2O3 for NO x Storage–Reduction (NSR) Catalysts

“…Potassium-and barium-containing compounds have been studied extensively for their NO x storage capacity [4]. The best performance of K as storage material, especially at high temperatures, is attributed to its stable nitrates [5]. Furthermore K 2 CO 3 is less toxic and cheaper than BaCO 3 .…”

Comparison of different kinetic models for NOX storage on a lean NOX trap

“…Models including nitrate formation and decomposition with rates dependant on the fraction of vacant sites and on the fraction of occupied sites (possibly raised to a power), respectively Shrinking core models where storage is limited by diffusion into the particles of storage media. A model describing diffusion into the washcoat with similar equations to the shrinking core models Microkinetic models …”

“…A model including surface, semi‐bulk, and bulk storage sites, with diffusion influencing the storage on the latter two Models with two discrete types of storage site to represent storage sites close to and far from the PGM sites or sites on two storage components (e.g., Ba and K sites, or Ba and Al 2 O 3 support sites) A model including diffusion of NO 2 from the PGM particles through/across the surrounding BaO phase/layer …”

“…In some models only NO 2 stores with NO needing to be oxidised to NO 2 before it can store, while in others direct storage of NO occurs as well; some studies have even lumped NO and NO 2 storage together …”

An Improved Model for NO x -Storage Catalysts

“…While several contributions concerning NSC-modeling have been published [1][2][3][4], only a few consider its full functionality. The different dynamics of storage and regeneration and the predictive description of the cyclic lean/rich-behavior including incomplete regeneration are still the main challenges.…”