Niobium-containing H3+xPW12-xNbxO40 (x=0, 1,2 and 3) Keggin and H6+xP2W18-xNbxO62 (x = 0, 1,2 and 3) Wells-Dawson heteropolyacids (HPAs) were prepared in this work to explore their redox properties and oxidation catalysis. Reduction potentials and absorption edge energies of H3+xPW12-xNbxO40 and H6+xP2W18-xNbxO62 HPA catalysts were measured by an electrochemical method and UV-visible spectroscopy, respectively. The trend of reduction potential is well consistent with the trend of absorption edge energy with respect to niobium substitution in both series of H3+xPW12-xNbxO40 and H6+xP2W18-xNbxO62 HPA catalysts. Absorption edge energy of H3+xPW12-xNbxO40 and H6+xP2W18-xNbxO62 HPA catalysts shifted to lower value with increasing reduction potential of the HPA catalysts, regardless of the identity of HPA catalysts; an HPA catalyst with higher reduction potential exhibited lower absorption edge energy. In order to probe oxidation catalysis of H3+xPW12-xNbxO40 and H6+xP2W18-xNbxO62 HPA catalysts, vapor-phase benzyl alcohol oxidation was carried out as a model reaction. Yield for benzaldehyde increased with increasing reduction potential and with decreasing absorption edge energy of H3+xPW12-xNbxO40 and H6+xP2W18-xNbxO62 HPA catalysts. (C) 2011 Elsevier B.V. All rights reserved.