Mechanochemical synthesis of efficient and stable cerium-based high entropy oxides (Ce₂FeCoNiMn)O_x for catalytic combustion of propane

Efficient catalytic combustion of light alkane remains a significant challenge in the field of air pollution control. High entropy oxide (HEO) catalysts have received recently much attention because of their excellent activity and stability. In this study, a series of Ce-based HEO catalysts of (Ce_nFeCoNiMn)O_x (n = 0, 1, 2, 4, 6) were synthesized via mechanochemical method. For the fluorite-type (Ce₂FeCoNiMn)O_x, the highest dopant content of four transition metals (Fe, Co, Ni, Mn) unexpectedly reached to about 67% into CeO₂ lattice by virtue of increased configurational entropy. The (Ce₂FeCoNiMn)O_x showed the best catalytic activity for propane combustion, and achieved 90% propane conversion at 309 ◦C, which was lower than that of the medium-entropy oxide (FeCoNiMn)O_x catalyst. This enhancement in activity can be attributed to the regulation of oxygen vacancies after transition metal doping and the excellent redox properties of transition metal elements themselves. Moreover, the (Ce₂FeCoNiMn)O_x exhibited good reactive stability even after five cycles due to entropy-driven structural stabilization. In situ diffuse reflectance infrared Fourier transform spectroscopy revealed that the catalytic oxidation of propane conforms to the Mars-Van Krevelen (MvK) mechanism, the formation of acetate and formate species was the critical steps, and their rapid decomposition maybe determined the total mineralization of propane.