The application of new catalysts based on high-entropy oxides to replace traditional catalysts has proven to be effective in both economics and energy. The present research focuses on the design and development of novel materials based on ultra-high-entropy rare-earth orthoferrites (UHE REOs, ∑REFeO₃) based on 16 rare-earth elements (RE = Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu). The solution combustion method was used to synthesize the ∑REFeO₃ nanopowder, which was then applied for catalytic hydrogen oxidation. By varying the ratio of fuel/oxidant (φ) towards values of 1.0 ÷ 3.5, six samples were obtained. It was found that the change in φ can lead to a difference in combustion mode and, therefore, result in the synthesized product's physicochemical properties. In particular, all these samples displayed an orthorhombic crystal structure of perovskite-like compounds with an average crystallite size of ∼31–36 nm and a specific surface area of ∼6.7–13.7 m² g⁻¹. The sample with φ = 2.0 showed its highest reducing property, as compared to those with φ = 1.0 and 3.0 when the total amount of H₂ consumption in the H₂-TPR analysis equals 2.75, 1.77, and 0.83 mL, respectively. Furthermore, the chemical phase purity, elemental composition, element oxidation state, and morphological features of the sample with φ = 2.0 were additionally examined by EDXS, XPS, and EDX-mapping analyses. The catalytic performance of the ∑REFeO₃ samples demonstrated that the sample with φ = 2.0 exhibits the highest activity, with a hydrogen conversion of ∼86% at 500 °C and an observed activation energy of 56.0 kJ mol⁻¹ (for a temperature region of 300–500 °C). Thus, this study highlights the great potential of UHE REOs as a catalytic platform for thermal hydrogen oxidation.

中文翻译：

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超高熵稀土正铁氧体（UHE REO）的结构和热氢氧化催化活性


应用基于高熵氧化物的新型催化剂替代传统催化剂已被证明在经济和能源方面都是有效的。目前的研究重点是基于16种稀土元素（RE = Sc、Y、La、Ce、Pr）的超高熵稀土正铁氧体（UHE REOs，ΣREFeO ₃ ）的新型材料的设计和开发、Nd、Sm、Eu、Gd、Tb、Dy、Ho、Er、Tm、Yb 和 Lu）。采用溶液燃烧法合成了ΣREFeO ₃纳米粉体，并将其用于催化氢氧化。通过将燃料/氧化剂的比率 ( φ ) 改变为 1.0 ÷ 3.5，获得了 6 个样品。研究发现， φ的变化会导致燃烧模式的不同，从而导致合成产品的物理化学性质的变化。特别是，所有这些样品都显示出类钙钛矿化合物的斜方晶体结构，平均晶粒尺寸为~31-36 nm，比表面积为~6.7-13.7 m ² g ^-1 。当H ₂ -TPR分析中H ₂消耗总量分别等于2.75、1.77和0.83mL时，与φ =1.0和3.0的样品相比， φ =2.0的样品显示出最高的还原性。此外，还通过 EDXS、XPS 和 EDX-mapping 分析检查了φ = 2.0 样品的化学相纯度、元素组成、元素氧化态和形态特征。 ΣREFeO ₃样品的催化性能表明， φ = 2.0 的样品表现出最高的活性，在 500 °C 下氢转化率为 ∼86%，观察到的活化能为 56.0 kJ mol ⁻¹ （对于温度区域） 300–500°C）。因此，这项研究凸显了 UHE REO 作为热氢氧化催化平台的巨大潜力。