Engineering Oxygen Vacancies of Co–Mn–Ni–Fe–Al High-Entropy Spinel Oxides by Adjusting Co Content for Enhanced Catalytic Combustion of Propane

Transition metal-based oxides with similar oxidation activities for catalytic hydrocarbon combustion have attracted much attention. In this study, a new class of metal high-entropy oxides (Co_<i>x</i>MnNiFeAl)₃O₄ (<i>x</i> = 1, 2, 3, 4, 5) with a porous structure was fabricated through a simple and inexpensive NaCl template-assisted sol-gel approach, which was employed for the catalytic oxidation of propane. The results indicated that the content of cobalt has a great impact on its activity, and the (Co₄MnNiFeAl)₃O₄ catalyst exhibited the best catalytic activity. At the high space velocity of 60 000 mL·g^-1·h^-1, the optimized one with high-temperature treatment can still achieve 90% propane conversion at 309 °C, which is 68 and 178 °C lower than those of the (CoMnNiFeAl)₃O₄ catalyst and pure cobalt oxide, respectively. Meanwhile, it has the lowest apparent activation energy (46.6 KJ·mol^-1) and the fastest reaction rate (26.976 × 10^-6 mol·g_cat^-1·s^-1 at 290 °C). The improved performance of the (Co₄MnNiFeAl)₃O₄ catalyst could be attributed to the enhancement of low-temperature reducibility, the increased number of reactive surface oxygen species, and the cocktail effect of the high-entropy oxides. This work provides new insights into the preparation of efficient light alkane degradation catalysts and a realistic approach for the large-scale application of high-entropy oxides in the field of oxidation catalysts.