In an oxidizing monolithic catalytic converter, mass transfer rates to the catalyst sites are greatest in the flow passage entrance regions. Segmenting the monolith, or slicing it normal to the flow direction and separating the pieces, increases conversion efficiency by forcing the species boundary layers to repeatedly redevelop. Models are presented which apply the heat transfer/mass transfer analogy to a developing flow correlation to provide an upper limit to conversion in a general monolith. The models predict that segmenting a small monolith into four pieces decreases hydrocarbon and carbon monoxide residuals by as much as 45 percent and 65 percent, respectively. Engine testing demonstrated 33 and 47 percent residual decreases.

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