Fabrication of FeO _x -ZrO ₂ nanostructures for automotive three-way catalysts by supercritical hydrothermal synthesis with supercritical CO ₂ drying

In this study, an inexpensive and abundant FeO _x -based catalyst was developed as a three-way catalyst (TWC). The deactivation associated with the fusion and aggregation of metallic iron under high-temperature reducing conditions was solved by the formation of FeO _x -ZrO ₂ nanostructures. Furthermore, high dispersibility of FeO _x in the nanostructures and multiple pores were successfully formed using a supercritical CO ₂ drying. As a result, the oxygen storage capacity of the FeO _x increased dramatically and high stability was obtained. In a TWC reactivity evaluation, the FeZr-TWC showed a high performance similar to that of the commercially available CeO ₂ -based TWC. Even after aging treatment for 20 h at 1000 °C under a 10 vol% steam condition, an NO _x (T ₈₀ , _NOx ) conversion of greater than 80% was successfully achieved, whereas it was not achieved by the standard TWC. Therefore, the FeZr nanostructures are expected to have sufficient capacity to replace the conventional CeO ₂ -based TWCs.