Kinetic Modeling Dynamic Oxygen Storage Capacity in Fresh and Aged Three-way Catalysts: Surface and Subsurface Oxygen Storage

Jian  Gong, Cummins Inc.

Three-way catalytic converter (TWC) has been widely and successfully utilized in stoichiometric gasoline and natural gas engines to control pollutants such as carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NOx). Oxygen storage capacity (OSC) is one of the most critical characteristics of a three-way catalyst (TWC) and is closely related to the catalyst aging and performance [1]. Accurate prediction of dynamic OSC is critical to TWC AFR control and TWC OBD development [2]. A dual-site oxygen storage model was developed to predict the dynamic oxygen storage on fresh and aged TWC catalysts [3]. Two oxygen storage sites (surface and sub-surface) were used to describe two distinct regimes of oxygen storage. A shrinking core diffusion model was applied on the sub-surface site to predict slow oxygen storage and depletion. Also, OSC measurement were conducted on a fresh and a aged TWC for model calibration. The amount of OSC was measured with distinct reductants over a temperature window of 100 °C to 600 °C. Two oxygen storage regimes were identified by analyzing the cumulative oxygen storage profiles. After bench aging at 955 °C for 57 hours, the amount of OSC decreased by 40%. The relationship between OSC and temperature was altered after aging. On the fresh TWC, the amount of OSC peaks at 400 °C and decreases at higher temperatures. However, the amount of OSC increases with temperature and reach a plateau at 600 °C on the aged TWC. Furthermore, the oxygen storage kinetics of the fresh and aged TWCs were analyzed. It was found that oxygen storage rate decreased significantly at temperature below 400 °C in kinetic regime while the oxygen storage rate decreases slightly in diffusion controlled regime. With the dual-site OSC model, the dynamic OSCs on the fresh and aged TWCs were correctly predicted. The change of the amount of oxygen storage sites as well as kinetic constants between the fresh and aged TWC were presented. The resulting dynamic OSC model can be implemented into the TWC model to predict TWC performance while probing the oxygen storage level of the TWC.


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[2]         Wang D, Li J, Gong J, Kamasamudram K, Currier N. Controlling Factors of Surface and Subsurface Oxygen Storage Capacity (OSC) of Three-Way Catalysts (TWCs) Used in Natural Gas Aftertreatment Systems. 2015 AIChE Annu. Meet. Proceeding, vol. 1, American Institute of Chemical Engineers; 2015, p. 396.

[3]         Gong J, Wang D, Li J, Currier N, Yezerets A. Dynamic oxygen storage modeling in a three-way catalyst for natural gas engines: A dual-site and shrinking-core diffusion approach. Appl Catal B Environ 2017;203:936–45. doi:10.1016/j.apcatb.2016.11.005.

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