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

Abstract

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 Ce_0.5Ni_0.1Mg_0.1Cu_0.1Zn_0.1Co_0.1O_x, cubic Zr_0.5Ni_0.1Fe_0.1Cu_0.1Mn_0.1Co_0.1O_x, spinel Ni_0.2Mg_0.2Cu_0.2Mn_0.2Co_0.2Al₂O_x, and perovskite LaNi_0.2Fe_0.2Co_0.2Cr_0.2Mn_0.2O_x, 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, Ce_0.5Ni_0.1Mg_0.1Cu_0.1Zn_0.1Co_0.1O_x with ordered macropores, active oxygen species, and high entropy-stabilized structure exhibits competitive activity (T₅₀ = 393 °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 °C), 3DOM-CeO₂ (T₅₀ = 506 °C), commercial CeO₂ (T₅₀ = 519 °C) and 1% Pt/Al₂O₃ (T₅₀ = 595 °C).