Oxygen Storage Property and Catalytic Performance of Ti-Doped FeNbO₄

Oxygen storage materials (OSMs) have potential applications in various fields, including catalysis, wherein a high oxygen storage capacity is desired because lattice oxygen and oxygen vacancies can act as reactants in catalytic reactions. In this study, we demonstrated that orthorhombic FeNbO4 has a high oxygen storage capacity, making it an effective catalyst for NO reduction and CO oxidation. FeNbO4 could release and store lattice oxygen via reversible topotactic transformations while maintaining cation ordering in its crystal structure. The lattice oxygen release properties were significantly enhanced by doping FeNbO4 with Ti at the Nb sites. The oxygen storage capacity of Ti-doped FeNbO4 was further improved by reduction and reoxidation pretreatments at 773 K, in which sufficient lattice oxygen was released under H2 atmosphere and reoxidized under O2 atmosphere. In NO reduction by CO in the presence of O2, Ti-doped FeNbO4 having high oxygen storage performance exhibited an excellent catalytic activity comparable to that of Pt/Al2O3, despite the absence of platinum group metals (PGMs). This could be explained by the participation of oxygen vacancies in the reaction via the Mars–van Krevelen mechanism, as revealed by temperature-programmed reactions with NO and CO. We propose that a catalyst design utilizing the highly reactive lattice oxygen and oxygen vacancies in OSMs can circumvent the need for expensive PGMs.