Precision Structure\nEngineering of High-Entropy Oxides\nunder Ambient Conditions

High-entropy oxides (HEOs) have unveiled a unique frontier\nin the\nrealm of heterogeneous catalysis, taking advantage of the entropic\neffect and increased complexities to deliver ultrahigh stability and\nlarge tuning capability. However, current HEO synthesis mainly relies\non high-temperature annealing approaches affording HEOs possessing\nno or low surface area, inferior active site exposure efficiency,\nand low controllability over the structure tuning. The grand challenge\nlies in producing high-quality HEO catalysts with high active site\nutilization efficiency, which relies on precision structure engineering,\npreferably under mild conditions. In this work, an in situ lattice\nengineering approach was developed to afford a supported HEO catalyst\nunder ambient conditions. The HEO compositions (CuCoFeNiMnO<sub><i>x</i></sub>) were uniformly integrated into the lattice of CeO<sub>2</sub> driven by cavitation-induced nucleation being generated via\nultrasonication. The as-afforded catalysts were featured by high surface\narea, atomically dispersed HEO compositions, active redox properties,\nabundant oxygen vacancies (O<sub>V</sub>), antiagglomeration, and\nhigh phase stability under harsh conditions. Compared with the ex\nsitu introduction of HEO on the surface, the in situ method provides\ndual benefits to maintain the dispersity of HEO via entropic and lattice\nconfinement effects. Engineering the complex HEO within the lattice\nof fluorite-structured CeO<sub>2</sub> also yields abundant defects\n(e.g., O<sub>V</sub>) and active metal sites with strong reducing\nproperties (e.g., Ce<sup>3+</sup> and Cu<sup>+</sup>), which greatly\nimproves the activity of the lattice oxygen and tunability of the\nadsorption behavior of the guest molecules, especially in the presence\nof impurities (e.g., water and propane). The catalytic performance\nof the supported HEO catalyst in oxidative procedures surpasses the\npure dense phase HEO as well as the ex situ-generated catalysts. The\nsynthesis approach being developed in this work, together with the\nfundamental understanding in structure evolution and reaction mechanism,\nshowcases a facile pathway under ambient conditions to generate stable\ncatalysts capable of maintaining structural robustness in high-temperature\nconditions while delivering enhanced catalytic performance.