X-ray standing wave (XSW) analysis and X-ray photoelectron spectroscopy are used to trace the electronicand atomic-scale structural changes of a supported vanadium oxide system at different stages of its oxidation−reduction cycle. Both the oxidation state and adsorption geometry of the vanadium oxide and its α-Fe2O3(0001) single crystal support show reversible changes through the oxidation−reduction cycle characteristicof catalytic behavior. The 3D V atomic distribution maps, derived from the summation of the XSW measuredFourier components, reveal that the V undergoes adsorption site exchange during the oxidation and reductioncycle.