CeO2-Grafted Mn-Fe Oxide Composites as Alternative Oxygen-Storage Materials for Three-Way Catalysts: Laboratory and Chassis Dynamometer Tests

A CeO2-grafted MnFeOy (CeO2/MnFeOy) has been developed as a substitute for the oxygen -storage CeO2 material in three-way catalysts. In the CeO2/ MnFeOy composite, CeO2 grains were intimately bound to the surface of the MnFeOy solid solution, which adopted an alpha-Mn2O3-type structure. Because the surface-grafted CeO2 acts as an oxygen gateway and MnFeOy acts as an oxygen reservoir, the combination of these oxides has a synergistic effect leading to the fast release and storage of a larger amount of oxygen compared with the separate constituents. The catalytic and oxygen release and storage performances of CeO2/MnFeOy were superior to those of CeO2/Fe2O3 in a previous study and were correlated to the contribution of Mn in the redox cycles. Finally, a real-sized honeycomb catalyst containing CeO2/MnFeOy was developed and tested using a vehicle driven on a chassis dynamometer in the JC08 (hot start) mode for gasoline engine vehicles (Japanese-type approval test cycle) and compared with a reference honeycomb catalyst containing CeO2. Despite a 30% decrease in the amount of CeO2, the developed honeycomb catalyst demonstrated high conversions of NOx, CO, and total hydrocarbons that were comparable with those of the reference honeycomb catalyst.