La1âxCaxFe1âxCoxO3 (x = 0.3, 0.5) perovskite-type oxide catalysts prepared by citric acid method were used for the steam reforming of ethanol (SRE) and oxidative steam reforming of ethanol (OSRE) to produce hydrogen. The anti-sintering and anti-coking properties of the catalysts for these two reactions have been investigated. The catalysts were characterized by temperature programmed reduction, X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy and thermal analysis techniques. The results indicated that the catalyst was highly selective to hydrogen, as well as very stable for OSRE reaction. The cobalt ions in the perovskite structure could be reduced to nanoparticles of metallic cobalt under the reduction atmosphere; the nano metallic cobalt could be oxidized and went back into the lattice of the perovskite structure under the oxidation atmosphere. The nanoparticles of metallic cobalt on the used catalyst could also be oxidized back into the perovskite structure. In the reaction process of OSRE, the cobalt species was possibly cycling as nanoparticles of metallic cobalt and cobalt ions in the perovskite structure, leading to its high anti-sintering stability.
                                    采用
柠檬酸法制备的 La1âxCaxFe1âxCoxO3 (x = 0.3, 0.5) 包晶型氧化物催化剂被用于
乙醇蒸汽转化(SRE)和
乙醇氧化蒸汽转化(OSRE)制氢。研究了这两种反应中催化剂的抗烧结和抗结焦性能。催化剂的表征采用了温度编程还原、X 射线衍射、X 射线光电子能谱、透射电子显微镜和热分析技术。结果表明,催化剂对
氢气具有高度选择性,而且对 OSRE 反应非常稳定。在还原气氛下,包晶结构中的
钴离子可以被还原成纳米
金属
钴颗粒;在氧化气氛下,纳米
金属
钴可以被氧化并回到包晶结构的晶格中。使用过的催化剂上的纳米
金属
钴颗粒也可以被氧化回到包晶结构中。在 OSRE 的反应过程中,
钴物种可能以
金属
钴纳米颗粒和
钴离子的形式在包晶结构中循环,因此具有很高的抗烧结稳定性。