Selective propene formation in periodic flow reactor: reducibility and catalytic activity of Ni–Mo–O system

Oxidative dehydrogenation (ODH) of propane with lattice oxygen of α-, α'- and β-NiMoO4 phases has been studied. Reduction tests of the different phases were performed by TG analysis under hydrogen at different temperatures. Under isothermal conditions lattice-oxygen-consumption rate was found to be higher on the β-phase with respect to the α- and α'-phases. TG analyses showed the existence of different sources of lattice oxygen in the catalyst, depending on the NiMoO4 phase. Catalytic activity was measured under steady state conditions, using a periodic flow reactor and it was then correlated to the reduction curve. It was found that the activation energy for ODH reaction over NiMoO4 of 54.3–62.7 kJ/mol is nearly identical to that obtained for the catalyst reduction under hydrogen (46–50.2 kJ/mol). The correlation between the activation energy of the reaction in a periodic operating system (POS) and that of solid reduction under hydrogen suggests that the reaction obeys a red–ox mechanism.