Ultrasound-mediated synthesis of nanoporous fluorite-structured high-entropy oxides toward noble metal stabilization

High-entropy oxides (HEOs) are an emerging class of advanced ceramic materials capable of stabilizing ultrasmall nanoparticle catalysts. However, their fabrication still relies on high-temperature thermal treatment methodologies affording nonporous architectures. Herein, we report a facile synthesis of single-phase, fluorite-structured HEO nanocrystals via an ultrasound-mediated co-precipitation strategy under ambient conditions. Within 15 min of ultrasound exposure, high-quality fluorite-structured HEO (CeHfZrSnErO_x) was generated as ultrasmall-sized particles with high surface area and high oxygen vacancy concentration. Taking advantage of these unique structural features, palladium was introduced and stabilized in the form of highly dispersed Pd nanoclusters within the CeHfZrSnErO_x architecture. Neither phase segregation of the CeHfZrSnErO_x support nor Pd sintering was observed under thermal treatment up to 900°C. The as-afforded Pd/CeHfZrSnErO_x catalyst exhibits good catalytic performance toward CO oxidation, outperforming Pd/CeO₂ of the same Pd loading, which highlights the inherent advantage of CeHfZrSnErO_x as carrier support over traditional oxides.