Engineering Morphology and Ni Substitution of NiXCo3-XO4 Spinel Oxides to Promote Catalytic Combustion of Ethane: Elucidating the Influence of Oxygen Defects

Transition metal oxides are potential alternatives to noble metal catalysts for oxidation reactions. Co-based spinel oxides, in particular, have attracted significant attention. Herein, NixCo3-xO4 catalysts were synthesized to elucidate the influence of oxygen vacancies on catalyst activities and reaction mechanisms for ethane combustion. A correlation between the activity and the population and properties of O defects was developed, with an increased number of O defects typically resulting in higher activity. Also, the shape-induced facet effect is related to the amount of Ni that is incorporated into the octahedral sites of Co oxide. The substituted Ni atoms altered the redox ability of NixCo3-xO4 by changing O vacancy formation and C-H bond dissociation. The NiCo2O4-TM catalyst (6.0 mmol mL-1 h-1) exhibits the highest activity for ethane oxidation compared with NiCo2O4-PC (0.5 mmol mL-1 h-1) and NiCo2O4-OL catalysts (1.3 mmol mL-1 h-1) at 330 degrees C, and its activation energy (Ea) is 70.9 kJ mol-1. No activity decay is observed after the initial transition stage of the reaction in a long-term stability test up to 500 h on the NiCo2O4- TM-coated monolith, either with or without water addition. A vacancy-mediated pathway was proposed according to in situ diffuse reflectance infrared Fourier transform (DRIFT) and density functional theory (DFT) calculations over the NiCo2O4(311) facet. Findings from this study expand our understanding of the facet-dependent catalytic behavior and ultimately enable the rational design of high-performance catalysts.

Automated summary

Transition metal oxides, particularly Co-based spinel oxides, have potential as alternatives to noble metal catalysts in oxidation reactions. In this study, NixCo3-xO4 catalysts were synthesized to investigate the influence of oxygen vacancies on catalyst activities and reaction mechanisms in ethane combustion. The activity was found to be correlated with the population and properties of O defects, with a higher number of defects resulting in increased activity. The shape-induced facet effect was also related to the amount of Ni incorporated into the octahedral sites of Co oxide. The findings from this study contribute to a better understanding of facet-dependent catalytic behavior and the design of high-performance catalysts.