Modeling the DOC

Richard  Blint, N2Kinetics Research, LLC

The diesel oxidation catalyst (DOC) is a relatively straightforward oxidation catalyst which can be described using simple global reaction mechanisms. That simplicity allows us to examine some of the basic expectations that we have for global reactions. Using prior kinetics development on DOC?s (Sampara, et al., Ind. Eng. Chem. Res., 46, 7993-8003, 2007, Sampara et. al, Ind. Eng. Chem. Res., 47, 311-322, 2008 and recent kinetics development using DOC SpaciMs measurements, Epling, et.al, Topics in Catalysis, 52, 1856-1859, 2009, K. Irani, master?s thesis, University of Waterloo, 2009) various aspects of global rate constants will be examined. The SpaciMs experimental work on species consumption in a diesel oxidation catalyst provides a spatial description of the decay of CO, H2, propylene and dodecane along the axis of a lightly loaded DOC monolith core. These SpaciMS measurements show distinctly different rates of consumption along the length of the catalyst channel with H2 showing decay at the lowest temperatures and dodecane and propylene decaying at higher temperatures. Also the CO decay shows distinctly different temperature dependence from the H2 consumption. Global kinetic rate constants have been independently developed from the SpaciMS spatial profiles. Modeling these profiles also allows a physical and spatial interpretation of the inhibition effects within the catalyst. For example, at a temperature of 200 oC, the CO is completely consumed half the distance down the channel indicating that the CO inhibition effect on the hydrocarbon consumption reactions is reduced for the last half of the catalyst. All of these ?integral reactor? effects shed light on the effects that cannot be included when reaction kinetic parameters are determined by modeling only the exit concentrations of a laboratory reactor.

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