Investigating niobium oxide-based materials: Synthesis, characterization, and applications in heterogeneous catalysis

In heterogeneous catalysis, the most stable form of niobium oxide (Nb2O5) and its hydrated form, niobic acid (Nb2O5·nH2O), have gained significant attention due to their unique structural, acidic, and redox properties. This review provides comprehensive details of recent developments pretaining to Nb2O5-based catalysis, beginning with a systematic discussion of the structural features of the niobium oxygen system, including Nb, NbO, NbO2, and Nb2O5. Further, Nb2O5‘s polymorphism highlighted the importance of structural variations and their impacts on observed catalytic performance. Similarly, the acidic and redox properties of Nb2O5 are analyzed in relation to coordination geometry, crystallinity, and surface defects. Further, various synthesis approaches are presented for controlling the morphology and phase composition of Nb2O5, including one-dimensional and two-dimensional nanostructures. The review further evaluates the application of Nb2O5 as a bulk catalyst, as a dopant to modify other supports, as a promoter to enhance metal dispersion or activity, and as a support for noble and base metals. Characterization techniques employed to probe structure, acidity, redox behavior, and reaction mechanisms are discussed, with particular attention to spectroscopic and in situ methods. Catalytic applications are reviewed across a wide range of reactions, including oxidation, dehydration, esterification, hydrogenation, NOx and CO2 reduction, and photocatalysis. The review distinguishes itself from earlier reports by offering a detailed and updated perspective that integrates structural chemistry with catalytic functions. By compiling these findings, the review aims to provide a foundation for the further development of Nb2O5-based materials in catalysis.