Abstract
Automotive exhaust gases containing harmful gases, such as hydrocarbons, CO, and NOx, are purified on a Pd-loaded catalyst. Since the purification efficiency depends on the oxygen concentration in the automotive exhaust gas, a material with a high oxygen storage performance is also essential for effectively purifying automotive exhaust gases. The present study demonstrates that the purification of the exhaust gases under fluctuating oxygen concentration proceeds efficiently on Pd/Ca2AlMnO5+δ which exhibits high oxygen release and storage capacities. Pd/Ca2AlMnO5+δ maintained reduction of NO to N2 for a longer time compared to conventional Pd/CeO2-ZrO2, under oxidative conditions. From the results obtained by combining operando and static X-ray absorption fine structure (XAFS) spectra, the valence state of the Mn species in the catalyst support was readily changed in response to the oxygen concentration in the exhaust gas, rather than that of the Pd species. In other words, the redox properties of the Mn species in Pd/Ca2AlMnO5+δ concern the NO reduction behavior under fluctuating oxygen concentration.
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