Clean Technology 2008
N. Kapur, L. Wang, T.J. Truex, K.L. Fujdala, J.B. Nicholas
Nanostellar Inc., US
monolith, modeling, CO oxidation, platinum
In order to fulfill the EPA emission standards for diesel automobiles, platinum-coated catalytic converters are commonly employed for CO and hydrocarbon oxidation. Mathematical models for monolith reactors can potentially shorten catalyst development time and provide optimized formulations for specific applications with respect to the washcoat variables. It is known that the catalytic performance can be optimized with respect to catalyst distribution on a monolithic substrate. Herein, we report the effect of catalyst distribution on the light-off temperature for CO oxidation in an axisymmetric, two-dimensional monolith reactor model under steady and transient conditions. Catalyst distribution schemes along both axial and radial washcoat directions are included in the mathematical model utilizing experimentally derived reaction rate laws for CO oxidation on platinum. A modest increase in outlet conversion can be obtained by redistributing the catalyst within washcoat layers in the radial direction at an elevated inlet gas temperature of 500 K. In addition, the light-off temperature for CO oxidation can be reduced by distributing the catalyst along the axial direction under steep inlet temperature ramp rates. The steep temperature ramp rates for inlet gases emulate the transient exhaust gas temperatures in vehicle testing (FTP) and normal operation and thus, the effects of catalyst zoning are applicable under cold start conditions.