Excellent Catalytic Activity of a Pd-Promoted MnOxCatalyst for Purifying Automotive Exhaust Gases

Currently, there is a strong demand for new automotive catalysts with improved low-temperature activity and reduced precious metal use. Such catalysts must undergo simultaneous CO/hydrocarbon oxidations and NO reduction. A Pd catalyst supported on Mn-modified hexagonal YbFeO3(Pd/Mn-YFO) exhibited extremely high activity at low temperature via a Mars-van Krevelen (MvK) mechanism involving lattice oxygen and oxygen vacancy site in the catalyst support. NO reduction proceeded by high CO and C(3)H(6)oxidation activity of Pd/Mn-YFO, and the catalytic activity of 1.0 wt% Pd/Mn-YFO was higher than that of 5.0 wt% Pd/Al2O3, despite the lower Pd loading. We clarified that the lattice oxygen in MnOx, which existed on the surface of YFO, consumed by CO and C(3)H(6)oxidation was recovered by NO to form N(2)via MvK-type NO reduction, while the Pd species promoted NO adsorption and dissociation on MnO-like species.