An advanced titration method during ethanol partial oxidation with tert-butanol is proposed to quantify the number of active redox sites in supported vanadia-titania catalytic systems (VOX/TiO2). In agreement with previous reports, our results indicate that not all vanadia atoms equally participate in the catalytic redox cycle. Therefore, the use of total vanadium loadings to calculate turnover frequencies results in an underestimation of actual turnover frequency values. The kinetically-relevant rate constants for ethanol partial oxidation obtained on the basis on the number of active sites calculated by our method indicate that these rate constants are independent of vanadia loading. This in turn suggests that the main species active for ethanol partial oxidation are well dispersed small sized vanadia clusters with a small number of V-O-V bridging bonds, predominant at low vanadia coverages. (C) 2017 Elsevier Inc. All rights reserved.