Improvement of NOx Performance and Thermal Stability in Pd-Based Catalyst 2000-01-2927
In order to improve the NOx performance and thermal stability of Pd-based catalyst, the effect of promoters was studied. The TWC performance, especially CO/NOx, and light-off were dramatically improved by the electronegative promoters. A ranking of the performance agreed with the electronegativity of the promoters.
It was found that the PdO decomposition temperature was shifted higher by the promoter and the shift was proportional to the electronegativity of the promoter. Therefore, it was suggested that a Pd sintering would be suppressed by the PdO stabilization. An advanced-2 catalyst design based on the above results showed an excellent performance.
The catalysts with this technology have been used for Japanese market and US LEV regulation since 1998. Furthermore, the technology has a potential for enhanced performance that can meet tighter regulation with lower Pd and Rh usage.