Oxygen Storage Property and Catalytic Performance of Ti-Doped FeNbO₄

Abstract

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 FeNbO 4 has a high oxygen storage capacity, making it an effective catalyst for NO reduction and CO oxidation. FeNbO 4 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 FeNbO 4 with Ti at the Nb sites. The oxygen storage capacity of Tidoped FeNbO 4 was further improved by reduction and reoxidation pretreatments at 773 K, in which sufficient lattice oxygen was released under H 2 atmosphere and reoxidized under O 2 atmosphere. In NO reduction by CO in the presence of O 2 , Ti-doped FeNbO 4 having high oxygen storage performance exhibited an excellent catalytic activity comparable to that of Pt/Al 2 O 3 , 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 temperatureprogrammed 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.