Study by electrical conductivity measurements of semiconductive and redox properties of M-doped NiO (M = Li, Mg, Al, Ga, Ti, Nb) catalysts for the oxidative dehydrogenation of ethane

Pure and M-doped nickel oxides with M = Li, Mg, Al, Ga, Ti, Nb, catalysts for the oxidative dehydrogenation of ethane into ethylene, were characterized by in situ electrical conductivity measurements. Their electrical conductivity was studied as a function of temperature and oxygen partial pressure and was followed with time during sequential exposures to air, an ethane-air mixture (reaction mixture) and pure ethane under conditions similar to those of catalysis. All the materials appeared to be p-type semiconductors under air with positive holes as the main charge carriers and their electrical conductivity decreased in the following order: Li-NiO > NiO > Mg-NiO > Nb-NiO > Ga-NiO > Al-NiO > Ti-NiO. All the catalysts remained p-type semiconductors in the reaction mixture at 400 degrees C. Correlations between the p-type semiconductivity and the catalytic properties have been evidenced. The reaction mechanism involves surface lattice O- species and can be assimilated to a Mars and van Krevelen mechanism.