Search Results

Dual-monolith catalyst systems containing Pd/Rh three-way catalysts (TWCs) provide effective emission solutions for LEV2/Bin 5 and Bin 4 close-coupled applications at low PGM loadings. These systems combine washcoat technology and PGM distribution for front and rear catalysts resulting in optimal hydrocarbon and NOx light-off and transient NOx control. The dual-catalyst [Pd/Rh + Pd/Rh] systems are characterized as a function of Pd-Rh content, PGM location, and catalyst technology for 4-cyl [close-coupled + underfloor] systems and 6-cyl close-coupled applications. The current Pd/Rh dual-catalyst converters significantly reduce NOx emissions compared to earlier [Pd + Pt/Rh] or [Pd + Pd/Rh] LEV/ULEV systems by utilizing uniform Rh distribution and new OSC materials. These new design strategies particularly impact NOx performance, especially during transient A/F excursions.

An investigation into the design, development and evaluation of a “new” washcoat technology family that enables significant reductions in rhodium usage levels has been concluded. These findings were demonstrated on three vehicle applications utilizing different calibration A/F control strategies. Additional testing investigated optimal Rh placement on a two brick catalyst system and the impact on FTP and US-06 test cycles. This study concludes with an evaluation of full useful life aged catalysts tested on 6 and 8 cylinder applications that are shown to have met Bin 4 FFV and ULEVII emission standards.

Three-way conversion (TWC) catalyst supports were prepared having CeO2-ZrO2 solid solution particles uniformly dispersed on γ-Al2O3 as discrete crystallites. The support morphology was characterized using STEM and TEM analysis. TPR and XRD analyses were also carried out on precious metal (PM) containing and PM-free samples before and after aging. These studies were combined with performance measurements which demonstrated the beneficial effects of solid solution formation on TWC catalyst activity. STEM and TEM analysis showed that well-dispersed CeO2-ZrO2 solid solution particles could be formed and simultaneously supported on a high surface area γ-Al2O3 support. For samples calcined up to 600°C, crystallite sizes of ≤50Å were formed as compared to sizes of over 200Å in the aged samples. The TPR studies suggested that for supports calcined up to 600°C most of the CeO2 present was reduced from the Ce4+ to the Ce3+ state in the temperature range 250 - 700°C.