Oxygen Gateway Effect of CeO₂/La₂O₂SO₄Composite Oxygen Storage Materials

Abstract

A synergistic enhancement in oxygen release/storage performance was achieved with composites formed between CeO₂ as an oxygen gateway and La₂O₂SO₄ as an oxygen reservoir. CeO₂ smoothly transfers oxygen atoms between La₂O₂SO₄ and the gas phase, whereas La₂O₂SO₄ stores a large amount of oxygen. The composite materials exhibited enhanced anaerobic CO oxidation and reversible oxygen storage in the presence of impregnated Pt catalysts as compared to their individual constituents (Pt/CeO₂ and Pt/La₂O₂SO₄). In situ X-ray diffraction and Raman experiments demonstrated that CeO₂ significantly accelerated the redox reaction between La₂O₂SO₄ (S⁶⁺) and La₂O₂S (S^2-), while preserving its structure. The reaction between CO and CeO₂/¹⁸O-labeled La₂O₂SO₄ composites suggested that CO mainly reacted with the lattice oxygen atoms of CeO₂, and the resulting oxygen vacancies were subsequently filled with oxygen atoms supplied by La₂O₂SO₄. This oxygen gateway effect of CeO₂ greatly enhanced the oxygen release/storage rates of La₂O₂SO₄, while maintaining the high oxygen storage capacity, which is an advanced feature of oxysulfate materials. The synergistic effect is mostly pronounced when the two different oxygen storage materials are in intimate contact to form a three-phase boundary.