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

It is anticipated that future gasoline engines will have improved mechanical efficiency and consequently lower exhaust temperatures at low load conditions, although the exhaust temperatures at high load conditions are expected to remain the same or even increase due to the increasing use of downsized turbocharged engines. In 2014, a collaborative project was initiated at Ford Motor Company, Oak Ridge National Lab, and the University of Michigan to develop three-way catalysts with improved performance at low temperatures while maintaining the durability of current TWCs. This project is funded by the U.S. Department of Energy and is intended to show progress toward the USDRIVE target of 90% conversion of hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NO_x) at 150 °C after high mileage aging. The testing protocols specified by the USDRIVE ACEC team for stoichiometric S-GDI engines were utilized during the evaluation of experimental catalysts at all three facilities. This paper summarizes work performed at Ford on the development of a catalyst formulation with significantly lower lightoff temperatures than a current production TWC after aging on a high temperature 4-mode durability cycle. The new catalyst consists of rhodium post-impregnated onto an overlayer of titanium deposited onto a silica-stabilized Al₂O₃ support. A rhodium loading study revealed that the lowest T90 s after 4-mode aging were obtained with 0.5% Rh. A titanium loading study showed that that the best performance after 4-mode aging was obtained with 8% titanium, which corresponded to the monolayer coverage of titanium. TEM analysis confirmed that the titanium monolayer remained well dispersed after the high temperature aging. A fresh sample of the optimized catalyst was evaluated after sulfur poisoning and after a stoichiometric desulfation.