Precursors of active Ni species in Ni/Al2O3 catalysts for oxidative dehydrogenation of ethane

Abstract

Ni/Al2O3 catalysts for oxidative dehydrogenation (ODH) of ethane were prepared by impregnation of Al2O3 with nickel acetate or nickel nitrate, and by mechanical mixing of NiO and Al2O3. The Ni-based catalysts were characterized by N2 adsorption-desorption, X-ray diffraction, diffuse reflectance UV-visible diffuse reflectance spectroscopy, and temperature-programmed reduction of hydrogen. The results showed that formation of crystalline NiO particles with a size of < 8 nm and/or non-stoichiometric NiO species in the Ni/Al2O3 catalysts led to more active species in ODH of ethane under the investigated reaction conditions. In contrast, tetrahedral Ni species present in the catalysts led to higher selectivity for ethene. Formation of large crystalline NiO particles (22–32 nm) over Ni/Al2O3 catalysts decreased the selectivity for ethene.