The influence of molybdenum, chromium and cobalt on the oxidation state and redox processes in V-Mg-O catalyst is studied by means of X-ray diffraction and electron spin resonance spectroscopy. The results obtained are correlated with catalytic activity and selectivity. It is shown that molybdenum doping increases the selectivity and the chromium and cobalt doping improves the activity of the catalyst studied. The promotional effect of the dopants on the catalytic mechanism is discussed.