Niobia catalysts can contain niobium oxide as a two-dimensional niobium oxide overlayer (surface niobia species), an oxide support (niobia supported surface redox sites) or a mixed oxide (solid solution or compound of niobium oxide). The molecular structures and redox properties of these different niobia-containing catalysts are investigated for several different oxidation reactions. These studies reveal that niobia present as surface metal oxide species, an oxide support and mixed oxides can directly as well as indirectly influence the redox properties of oxide catalysts.