Investigation of\nthe Effect of the Third Cation M\n(M = Mg, Al, Mn, and Fe) on the Properties and Catalytic Behavior\nin Ethane Oxidative Dehydrogenation of M‑NiNbO Mixed Oxides

This work examines the effect of incorporating a third\ncation M\n(M = Mg, Al, Mn, or Fe) into Nb-promoted NiO catalysts (Ni<sub>0.85</sub>Nb<sub>0.15</sub>O) on their physicochemical properties and catalytic\nperformance in the oxidative dehydrogenation (ODH) of ethane into\nethylene. Therefore, a series of mixed oxides with the composition\nNi<sub>0.765</sub>Nb<sub>0.135</sub>M<sub>0.1</sub>O was synthesized,\ncharacterized, and analyzed for catalytic behavior. The addition of\nthe third cation markedly modified the redox and semiconductive properties\nof the catalysts, thus affecting their ODH performance. The selectivity\ntoward ethylene was strongly dependent on the cation modifier, as\nit modulated the density of nonselective sites on the catalyst surface.\nIn the low-temperature region, Mn-NiNbO demonstrated the highest conversion\nrates but with the lowest ethylene selectivity, whereas Fe-NiNbO,\ndespite being less active than the undoped NiNbO, exhibited the highest\nethylene selectivity. Overall, undoped NiNbO emerged as the best catalyst\nin terms of both activity and selectivity at isoconversion. All catalysts\nunderwent partial reduction under reaction conditions, with the degree\nof reduction inversely correlated with the specific reaction rates.\nAlthough none of the catalysts remained stable at 400 °C, Al-NiNbO\nshowed the least deactivation over time. The deactivation was linked\nto a reduction in p-type conductivity and a loss of redox functionality\nduring operation.