The Development of Low Temperature Three-Way Catalysts for High Efficiency Gasoline Engines of the Future

In anticipation that future gasoline engines will have improved fuel efficiency and therefore lower exhaust temperatures during low load operation, a project was initiated in 2014 to develop three-way catalysts (TWC) with improved activity at lower temperatures while maintaining the durability of current TWCs. This project is a collaboration between Ford Motor Company, Oak Ridge National Laboratory, and the University of Michigan and is funded by the U.S. Department of Energy. The ultimate goal is to show progress towards the USDRIVE goal of 90% conversion of hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NO_x) at 150°C after high mileage aging. A reactor was set up at Ford to follow the catalyst testing protocols established by the USDRIVE ACEC tech team for evaluating catalysts for stoichiometric gasoline direct-injection (S-GDI) engines; this protocol specifies a stoichiometric blend of CO/H₂, NO, C₃H₆, C₂H₄, C₃H₈, O₂, H₂O, and CO₂ for the evaluations. This paper summarizes some of the lessons learned from the reactor testing at Ford and also discusses the results on some initial catalyst formulations at Ford that consisted of palladium (Pd) on various oxide supports. The temperature ramp rate had little effect on the lightoff performance, but the O₂ level around stoichiometry and interactions between the gas species were found to significantly affect the light off temperatures. Al₂O₃ and ZrO₂ catalysts with 2% Pd were fairly robust to lean aging at 1000°C, but a TiO₂ powder with 2% Pd suffered significant degradation after lean aging at only 800°C.