Incorporating three-dimensional ordered macropores into high-entropy oxides for catalytic soot combustion

Since 2018, high entropy oxides (HEOs) have been introduced to the catalysis community, due to their tunable compositions, abundant lattice distortion, and excellent thermal stability. Although porous structure is usually essential for heterogeneous catalysts, the synthesis of porous HEOs using both traditional hard and soft templates failed. Herein, inspired by the self-assembly behavior of polystyrene (PS), various HEOs with three-dimensional ordered macro-porous (3DOM) structure, including cubic Ce0.5Ni0.1Mg0.1Cu0.1Zn0.1Co0.1Ox, cubic Zr0.5Ni0.1Fe0.1Cu0.1Mn0.1Co0.1Ox, spinel Ni0.2Mg0.2Cu0.2Mn0.2Co0.2Al2Ox, and perovskite LaNi0.2Fe0.2Co0.2Cr0.2Mn0.2Ox, were prepared. Together, the uniform distribution of metal precursors inside the PS matrix and the decreased crystallization temperature due to the increased configuration entropy facilitated the formation of 3DOM-HEOs. The crystallization process was monitored by in situ X-ray diffraction. Interestingly, Ce0.5Ni0.1Mg0.1Cu0.1Zn0.1Co0.1Ox with ordered macropores, active oxygen species, and high entropy-stabilized structure exhibits competitive activity (T50 = 393 & DEG;C) in soot combustion under harsh conditions (4.2 vol% moisture, 20 ppm SO2), higher than those of the sol-gel control sample (T50 = 419 & DEG;C), 3DOM-CeO2 (T50 = 506 & DEG;C), commercial CeO2 (T50 = 519 & DEG;C) and 1% Pt/Al2O3 (T50 = 595 & DEG;C). An ordered macro-porous structure is achieved for various types of HEOs including cubic, perovskite, and spinel crystal patterns by polystyrene crystal templating. The prepared HEOs displayed excellent catalytic performance in soot combustion.