Steady state and lean-rich cycling study of a three-way NOX storage catalyst: Modeling

Abstract

A nonisothermal monolithic reactor model with a global kinetic formulation is developed to predict the steady-state and cyclic oxidation and reduction with CO and H2 of a model three-way NOx storage catalyst (TWNSC). Data were used from a parallel experimental study conducted by Malamis et al. [1] along with kinetics measurements made in the current study. The reactor model comprises a low-dimensional treatment of the transport processes and multi-site NOx and O2 storage combined with catalytic kinetics of the reaction steps. Kinetic sub-models of NO and CO single and co-oxidation are developed to capture the CO and NO light-off trends including inhibition effects. The sub-models are combined to simulate the catalyst performance under both steady-state and cyclic conditions. The TWNSC model predicts the steady-state product distribution spanning a range of rich conditions, along with cyclic operation features, including cycle-averaged NOx conversion and NH3 selectivity, and the transient species concentrations and temperature profiles over a wide range of total cycle time (TCT, 10 s–200 s) at 50% duty cycle rich. The model captures the key feature of the TWNSC using CO and H2 as reductants. The results point to the importance of sizing the TWNSC for either NO reduction to N2 or NH3 formation, depending on the application. The TWNSC reactor model provides insight about reaction and transport interactions, spatio-temporal features, etc., along with guidance in the catalyst design and operation strategy optimization.