Synthesis of Hexagonal YbMnO3 and Its Three-Way Catalytic Performance

For stringent regulations of exhaust gases from gasoline-powered vehicles, small amount of platinum-group metals (PGMs) in automotive catalysts is highly required. To satisfy this requirement, applications of base-metal catalysts such as Fe and Mn have been vigorously discussed and investigated. Previously, we reported that rare earth metals containing hexagonal Fe and Mn oxides work as effective support materials and active species in CO oxidation, C3H6 oxidation, and NO reduction. However, most of the base-metal oxides could be readily decomposed by gasoline engine aging at approximately 1000 degrees C. In this study, we show that hexagonal YbMnO3 (h-YbMnO3) can be obtained as single-phase using the simple coprecipitation method with H2O2. Moreover, h-YbMnO3 can function as a oxygen storage material, which maintains its hexagonal structure after hydrothermal aging at 1000 degrees C for 25 h owing to the small ionic radius of Yb. On the other hand, isostructural YMnO3 (h-YMnO3) can be easily decomposed under the same aging condition. The catalytic performances of Pd loaded materials (Pd/h-YbMnO3, Pd/Al2O3, and Pd/CeO2-ZrO2 (CZ)) on cordierite honeycomb substrates were evaluated. Among them, Pd/h-YbMnO3 exhibited the highest oxidation activities even though it had significantly lower specific surface area (SSA). In particular, Pd/h-YbMnO3 exhibits a strong effect on paraffin oxidation such as C3H8, which is less reactive than other olefinic and aromatic hydrocarbons for automotive catalysts.

Automated summary

To meet the stringent exhaust gas regulations for gasoline-powered vehicles, the use of platinum-group metals (PGMs) in automotive catalysts is necessary. However, the feasibility of using base-metal catalysts such as Fe and Mn has been explored, with rare earth metals containing hexagonal Fe and Mn oxides showing promise. This study focuses on the stability and catalytic performance of hexagonal YbMnO3 (h-YbMnO3) as compared to isostructural YMnO3 (h-YMnO3) under gasoline engine aging conditions, and demonstrates that Pd loaded Pd/h-YbMnO3 exhibits the highest oxidation activities for paraffin oxidation in automotive catalysts.