(563d) Measuring and Using Reaction Gradients In Diesel Emissions Reduction Catalysts

In this presentation, reaction gradients that exist within lean-NOx trap (LNT) catalysts, selective catalytic reduction (SCR) catalysts and diesel oxidation catalysts (DOCs) will be discussed. Furthermore, results obtained after simulated degradation will also be presented, describing how reactivity within the catalysts change. With the DOC data, modeling was used to predict the performance of DOCs with tailored-designs in axial active site gradients. The results clearly show that tuning the active site distribution along the length of the catalyst can lead to significant changes in performance, indicating the precious metal contents could be optimized in automotive catalytic converter or diesel engine aftertreatment technologies. The results demonstrate that under conditions where the catalyst is challenged (i.e. high flow, low active site loading, slow temperature ramp rate etc) the differences between the catalyst designs are more evident. These trends are based on the significance of the impact of (1) convective heat transfer from the incoming gases during warm-up that are carrying increasing heat content versus (2) the exotherm generated by oxidation of the reactant gases as well as the self-poisoning effects of the key reactants (i.e. CO, C₃H₆ or NO). Again, degradation was also evaluated and the data clearly demonstrate that different designs are “optimal” depending on the key degradation mode and/or its reversibility. Experimental data with a zone-coated diesel oxidation catalyst will also be presented, with axial reactivity profiles also used to describe its superior performance.