Origin of electronic structure dependent activity of spinel ZnNi_xCo_2-xO₄ oxides for complete methane oxidation

Exploring active and low-cost spinel catalysts for complete methane oxidation is essential for the development of efficient air purification technologies. Herein, a series of spinel oxides ZnNi_xCo_2-xO₄ (x = 0–0.8) were synthesized to investigate the origin of their electronic structure dependent activities and mechanisms for methane oxidation. The interplay between O p-band center and M_oct d-band center was found to be responsible for the methane oxidation activity. Ni-poor ZnNi_xCo_2-xO₄ spinels with the M_oct d-band center positioned higher relative to the O p-band center, exhibited greater metal character, indicative of a dissociative adsorbed oxygen featured suprafacial Eley-Rideal (E-R) model. In contrast, Ni-rich ZnNi_xCo_2-xO₄ with the O p-band center in a higher position relative to the M_oct d-band center, displayed greater oxygen character, predominated by the intrafacial Mars-van-Krevelen (Mv-K) mechanism featuring the involvement of lattice oxygen. These findings may provide steps towards the rational design of better spinel oxides for catalytic oxidation reactions.