Comparison of Pd-only, Pd/Rh, and Pt/Rh Catalysts in TLEV, LEV Vehicle Applications - Real Vehicle Data versus Computer Modeling Results

The following paper highlights the results of a vehicle emission improvement program with emphasis on two main points:

In the initial phase, various combinations of Pd and Pt-based three-way catalyst technologies were evaluated on a TLEV and a LEV calibrated vehicle in order to generate ULEV exhaust gas levels. One goal in this portion of the study was to achieve technical equivalence between a viable Pd-based technology and a newly developed Pt-based technology. A combination of the Pd- and Pt-based technologies was able to meet the ULEV and part of the ULEV II regulations in the test vehicle after a catalyst aging cycle that resembles 50,000 miles of vehicle driving.

In the later phase, a mathematical algorithm based on the original TLEV and LEV vehicle data was developed in order to conduct computer modeling of the exhaust gas aftertreatment system. This algorithm described the kinetic behavior of the individual catalysts over a broad range of reaction conditions. This model was then validated by comparing the experimental results of the LEV vehicle over the FTP-75 cycle to the theoretical predictions of the computer. Furthermore, a sensitivity study was conducted - e.g. focusing on various exhaust gas inlet conditions or different catalyst volumes - in order to identify the most potential parameters for a system optimization.

This effort proved that there is a good correlation between the experimental and calculated results for the LEV certified vehicle. The data of the sensitivity study will be discussed in further detail, mainly focussing on the HC and NO_x emissions