Unraveling the contribution of structural phases in Ni–Nb–O mixed oxides in ethane oxidative dehydrogenation

Abstract

The role of each structural phase present in highly active and selective Ni0.85Nb0.15 catalyst in ethane oxidative dehydrogenation is investigated. Based on previous studies, Ni0.85Nb0.15 consists of a Ni–Nb solid solution and a Nb-rich amorphous phase. A series of Ni-based mixed oxides with low Nb content simulating the Ni–Nb solid solution and an amorphous Nb-rich sample were synthesized and studied separately. The catalytic tests demonstrated that the introduction of even a tiny amount of Nb (atomic ratio: Nb/(Ni+Nb)=0.01) leads to a drastic increase in ethylene selectivity (150%) compared to pure NiO. Selectivity gradually increases with increasing Nb loading up to 15%, in parallel with the decrease in oxygen desorbed as measured by O2-TPD. Based on the results of combined catalytic testing and physicochemical characterization, Ni–Nb solid solution can be identified as the key component for the high ethylene selectivity of the Ni0.85Nb0.15 catalyst, as the insertion of even a small amount of Nb drastically decreases the electrophilic oxygen species responsible for the total oxidation reactions. Co-existence of the Ni–Nb solid solution with the amorphous Nb-rich phase does not influence significantly the catalytic properties of the material.