The role of ceria in TWC catalysts beyond oxygen storage

Paper #:
  • 2018-01-0963

Published:
  • 2018-04-03
Abstract:
Ceria-zirconia mixed oxides are known to perform as oxygen storage catalyst in exhaust after treatment catalytic devices such as three way catalytic converters (TWC). They are furthermore used as promotor material of precious-metal catalysts for the water-gas-shift (WGS) reaction and as NOx storage compound in lean NOx traps (LNTs). Although widely used, the chemical background of the beneficial properties of the ceria-zirconia mixed oxides is still not fully understood. Several different kinetic mechanisms are available in the literature differing in complexity and in the considered species. Numerous studies about the oxygen storage dynamics focus on the activity of ceria-zirconia mixed oxides in function of their composition and the content of different noble metals such as palladium, platinum, and rhodium; while others examine the influence of the preparation method. Here, a comprehensive kinetic model involving NOx, CO, and oxygen storage and release, is validated against experimental data of a TWC after a four-stroke engine test bench. The simulations are performed using a 1D single-channel model. The role of two different oxygen storage sites (surface and sub-surface) and the oxidation of reduced ceria by H2O and CO2 is discussed. The results of the transient experiments are well reproduced by the kinetic model.
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