Potassium addition has different influence on the selectivity to isobutene in oxidative dehydrogenation of isobutane for the two chromium based catalysts: the decrease for CrOx/Al2O3(CrAl) and the increase for CrOx/TiO2(CrTi). This contrary effect of potassium was found to be associated with the increase in the rate of oxygen chemisorption (equivalent to the rate of reoxidation) and the increase in coverage with oxygen for CrAl, and with the decrease of these parameters for CrTi catalyst. Acid-base properties, determined by isopronanol decomposition and reducibility, estimated from TPR data, seem to affect less the catalytic properties, since they change on the potassium addition in the same way: acidity and reducibility decrease and basicity increases in the K-doped catalysts. Electron work function was found to decrease for potassium doped CrAl and did not change for CrTi catalyst. (C) 2010 Elsevier B.V. All rights reserved.