Abstract

Self-oscillatory methane oxidation over Ni foil at 750°C for 1 h resulted in the formation of a porous layer with a depth of 10–12 μm. The layer depth did not increase as the self-oscillatory reaction time was increased to 2–3 h. The porous layer consisted of nickel oxide crystals 100–200 nm in size or metallic Ni crystallites (indistinct crystals) of the above size in an oxidative gas atmosphere or a reducing atmosphere, respectively. The formation of the layer caused a great increase in the catalytic activity of nickel in the carbon dioxide conversion of methane (CDCM). Immediately after the self-oscillatory reaction, the crystals in the porous layer were in an oxidized state. In this state, they can remain at 750°C in a flow of an inert gas or CO₂ without catalytic activity losses. On the contrary, the oxide crystals were reduced to the metal in a reducing atmosphere (H₂, CH₄), and they gradually stuck together to form a spongy structure whose surface area was much lower than that of the initial oxidized sample. A decrease in the catalytic activity of nickel after reducing pretreatment and in the course of the catalytic CDCM (where the catalyst was also reduced) confirmed the above conclusion. The porous layer on the Ni surface was similar to a Ni foam sample with pores of ~1 μm (metallic membrane) in catalytic and reactive properties, but it differed in a limited depth on the surface of the bulk metal.

中文翻译：

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自振荡甲烷氧化过程中形成的镍表面层的研究

摘要

镍箔在750°C的温度下甲烷自振荡甲烷氧化1 h，形成了深度为10–12μm的多孔层。随着自激振荡反应时间增加到2-3小时，层的深度没有增加。多孔层分别由大小为100-200 nm的氧化镍晶体或具有上述大小的金属Ni微晶（模糊晶体）组成，分别位于氧化性气体气氛或还原性气氛中。该层的形成导致甲烷的二氧化碳转化（CDCM）中镍的催化活性大大提高。自振荡反应后，多孔层中的晶体立即处于氧化状态。在这种状态下，它们可以在惰性气体或CO ₂的流中保持在750°C的温度下。没有催化活性的损失。相反，在还原气氛（H ₂，CH ₄）中，氧化物晶体被还原为金属，并且它们逐渐粘附在一起以形成海绵状结构，其表面积比初始氧化样品的表面积低得多。在还原预处理之后以及在催化CDCM过程中（其中催化剂也被还原）镍的催化活性降低证实了上述结论。Ni表面上的多孔层类似于具有约1μm孔（金属膜）的Ni泡沫样品，其催化和反应性能不同，但在大块金属表面的深度有限。