The present work has demonstrated the large-capacity oxygen storage of various isomorphous lanthanide oxysulfates, Ln2O2SO4 (Ln = La, Pr, Nd and Sm), which utilize the nonmetallic element (S) as a redox site instead of metallic cations. The reduction by H2 or hydrocarbons and subsequent reoxidation by O2 between Ln2O2SO4(S6+) and Ln2O2S(S2-) achieved an oxygen storage of 2 (mol of O2)·mol-1, which is 8 times larger than that of the conventional CeO2−ZrO2 material. Although the reversible redox cycle of thermostable Ln2O2SO4 with Ln = La, Sm, and Nd was possible only at high temperatures above 700 °C, the Pr system could work at an exceptionally low temperature of ca. 600 °C. Furthermore, the redox of the Pr system could be accelerated in the presence of impregnated noble metals (1 wt % Pd), which supply activated hydrogen as well as oxygen by spillover. Because the elimination of a large amount of sulfate species as SO2/O2 from the bulk crystallites of sulfate precursors yields the macroporous texture of Ln2O2SO4 and Ln2O2S with a high specific surface area, the resultant rapid gas diffusion as well as solid−gas reactions would facilitate the oxygen storage and release processes.

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A sulfur redox cycle between La(2)O(2)SO(4)(S(6+)) and La(2)O(2)S(S(2-)) phases was found for the first time to achieve the oxygen storage of 2 mol O(2) mol(-1), which is eight times larger than that of the conventional CeO(2)-ZrO(2) system.

Novel Oxygen Storage Mechanism Based on Redox of Sulfur in LanthanumOxysulfate/Oxysulfide. -A large O 2 storage capacity of 2 mol O 2 /mol storage material without losing the sulfur content is achieved based on a sulfur redox cycle in the La2O2S (S 2-)/La2O2SO4 (S 6+ ) system. This is the first example of oxygen storage that uses non-metallic elements as a redox site. The oxygen storage capacity is eight times larger than that of the conventional CeO 2 -ZrO 2 system. Oxygen storage materials seem to be useful not only for automotive catalysts, but also for other high-temperature processes, where instant oxygen scavengers are required. The new system will contribute to further development of oxygen storage materials and their applications. -(MACHIDA*, M.; KAWAMURA, K.; ITO, K.; Chem.