Oxygen Gateway Effect of CeO₂/La₂O₂SO₄ Composite Oxygen Storage Materials

摘要

A synergistic enhancement in oxygen release/storage performance was achieved with composites formed between CeO_(2) as an oxygen gateway and La_(2)O_(2)SO_(4) as an oxygen reservoir. CeO_(2) smoothly transfers oxygen atoms between La_(2)O_(2)SO_(4) and the gas phase, whereas La_(2)O_(2)SO_(4) 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/CeO_(2) and Pt/La_(2)O_(2)SO_(4)). In situ X-ray diffraction and Raman experiments demonstrated that CeO_(2) significantly accelerated the redox reaction between La_(2)O_(2)SO_(4) (S~(6+)) and La_(2)O_(2)S (S~(2–)), while preserving its structure. The reaction between CO and CeO_(2)/~(18)O-labeled La_(2)O_(2)SO_(4) composites suggested that CO mainly reacted with the lattice oxygen atoms of CeO_(2), and the resulting oxygen vacancies were subsequently filled with oxygen atoms supplied by La_(2)O_(2)SO_(4). This oxygen gateway effect of CeO_(2) greatly enhanced the oxygen release/storage rates of La_(2)O_(2)SO_(4), 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.