Multifunctional Aspects of Three-Way Catalyst: Effects of Complex Washcoat Composition

Abstract

In this paper multifunctional aspects in operation of Pt/Rh/Ce/γ-Al 2 O 3 three-way catalyst (TWC) are discussed on the basis of computed spatiotemporal patterns of reacting and deposited species on specific active sites distributed in the catalytic washcoat layer. A spatially pseudo-one-dimensional, heterogeneous model of a TWC reactor has been developed, with well-mixed gas phase and description of diffusion in the porous catalytic washcoat. The model includes a detailed non-stationary kinetic scheme for CO and C 2 H 2 oxidation, oxygen storage on CeO 2 , CO 2 adsorption on the support and NO x transformation and reduction. Pt, Rh, Ce and γ-Al 2 O 3 sites are considered with different kinetic parameters. A methodology is developed for the studies of the effects of internal diffusion and washcoat composition (i.e. concentration and distribution of active Pt, Rh and Ce catalytic sites) on the conversion of main pollutants in automobile exhaust gas under transient conditions. Several cases of variable distribution of the catalytic sites in the washcoat layer are discussed with respect to the reactor performance. Effects of oscillations in the inlet oxygen concentration are studied. Complex interactions, particularly between reaction intermediates and the stored oxygen within the washcoat, cause the increase of conversions in the periodic operation when compared with the stationary one.