Abstract

The oxidation of propane was studied over Ni foil, a thick Ni/Si film, and a thin Ni/Si film in a flow reactor under oxygen-deficient conditions at a total pressure near 1 mbar. The thickness of the foil was 125 µm, while the thickness of the films was 20 and 1.5 µm, respectively. It was shown that regular self-sustained reaction-rate oscillations arise only over the Ni foil and the thick Ni/Si film. The relaxation-type oscillations appear at 700 °C after an induction period of approximately 50 min, which is accompanied by the formation of a rough and porous structure over their surfaces. According to krypton adsorption measurements, the effective surface area of the treated catalysts increases significantly. CO, CO₂, H₂, and H₂O were detected as products in the gas phase. The results of operando X-ray absorption spectroscopy study indicate that the oscillations originate due to periodical oxidation and reduction of nickel. The highly active state is Ni in the metallic state, while the transition to the poorly active state is accompanied by the growth of NiO layer on the catalyst surface. The upper layer of the catalysts with a thickness of at least 15 nm is involved in the oxidation/reduction process. In contrast, no oscillations appeared in the oxidation of propane over the thin Ni/Si film. In this case, the thickness of the Ni layer is not sufficient for the formation of a porous structure over the thin Ni film. As a result, the thin Ni film cannot provide high activity in the catalytic oxidation of propane that is sufficient for the self-sustained oscillations to occur. The reasons that lead to oscillatory behavior in the oxidation of propane over nickel are discussed.

Graphic Abstract

中文翻译：

---

镍箔和薄膜上丙烷氧化中的振荡行为

摘要

在缺氧条件下，在总压力接近1 mbar的条件下，在流动反应器中研究了Ni箔，Ni / Si厚膜和Ni / Si薄膜上丙烷的氧化。箔的厚度为125μm，而膜的厚度分别为20和1.5μm。结果表明，只有在镍箔和厚厚的镍/硅膜上才会出现规则的自持反应速率振荡。在大约50分钟的感应时间后，松弛型振荡出现在700°C，并伴随在其表面形成粗糙而多孔的结构。根据k吸附测量，处理过的催化剂的有效表面积显着增加。CO，CO ₂，H ₂和H ₂在气相中检测到O为产物。结果operandoX射线吸收光谱研究表明，振荡起因于镍的周期性氧化和还原。高活性态是金属态的Ni，而向低活性态的转变伴随着催化剂表面NiO层的生长。氧化/还原过程涉及厚度至少为15nm的催化剂的上层。相反，在Ni / Si薄膜上的丙烷氧化没有振荡。在这种情况下，Ni层的厚度不足以在薄Ni膜上形成多孔结构。结果，Ni薄膜不能在丙烷的催化氧化中提供足以使自持振荡发生的高活性。

图形摘要