一氧化碳偶联制草酸二乙酯用Pd-Fe/α-Al_2O_3催化剂的表面结构

Surface Structure of Pd-Fe/α-Al_2O_3 Catalyst for CO Coupling to Diethyl Oxalate

应用XPS ,XRD ,TEM和TPR等表征技术研究了CO常压气相偶联合成草酸酯反应体系中Pd Fe/α Al2 O3 催化剂的表面结构 .结果表明 ,催化剂表面的活性组分钯以高度分散的Pd0 形式存在 ,分散的钯微晶平均粒径约为 8nm ;助剂铁以Fe2 +形式存在 ,其分散度极高 .根据表征实验结果 ,讨论了活性组分、助剂和载体三者之间的相互作用 .助剂可以优先高度分散在载体表面 ,而活性组分会自动落位在助剂层上达到均匀分散 ,即催化剂表面形成了类似于金属 金属氧化物 载体相间的结构 .

In the past decades, a new environmentally benign chemical process to synthesize diethyl oxalate(DEO) by catalytic coupling reaction of CO in gaseous phase at normal pressure has attracted great interest of many researchers in the world. In our previous work, the Pd-Fe/α-Al 2O 3 catalyst for synthesis of DEO exhibited high catalytic activity, high selectivity and fair stability. To continue fundamental research on the catalytic reaction, the surface structure of Pd-Fe/α-Al 2O 3 catalyst was studied by temperature-programmed reduction (TPR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) techniques. The results showed that the highly despersed active component palladium on the catalyst surface is in Pd0 state and its average size is ca 8 nm, the promoter iron is in Fe 2+ state and has higher dispersion than palladium on the surface of α-Al 2O 3 support. The interactions of the active component, the promoter and the support of the catalyst were discussed. It was concluded that the promoter iron is preferentially dispersed on the support until nearly single layer coverage is reached and the active component palladium locates on the FeO layer owing to the differences between their interactions. That is to say, an FeO layer on the catalyst surface is present as an interface between Pd and α-Al 2O 3.