Supported catalysts with 5 wt.% V2O5 on CexZr1-xO2 (x= 1, 0.9, 0.8, 0.7, 0.5, 0.3 and 0) have been prepared and tested in selective catalytic reduction (SCR) of NO by NH3 between 100 and 300 degrees C at a GHSV of 70000 h(-1). They were also characterized with regard to phase composition, structure of VOx sites and valence state of vanadium, cerium and zirconium using XRD, ICP-OES, XPS, UV-vis-DRS and EPR, partly in situ. ViCe(0.2)Zr(0.3)O(2) showed highest activity, N-2 selectivity and stability with almost 100% NO conversion to N-2 at 220 degrees C and no deactivation during 190 h on stream at 250 degrees C. Besides high V/(Ce + Zr) surface ratio, fast and reversible VOx redox cycles revealed to be essential for active catalysts, while Ce and Zr seem to stay tetravalent under reaction conditions. Both, catalytic activity as well as VOx reduction/reoxidation rates decrease in the order ViCe(0.2)Zr(0.3)O(2) > V/ZrO2 > V/CeO2. In the best catalyst ViCe(0.2)Zr(0.3)O(2), active VOx sites are effectively connected to the support surface, probably within O-Ce-O-V(=O)-O-Zr-O-moieties that may support oxygen transport, which is relevant for high SCR activity. (C) 2016 Elsevier B.V. All rights reserved.