钾助催化剂与Fe3O4相互作用行为的XRD表征

XRD研究表明 ,作为乙苯脱氢催化剂中的氧化铁活性组分 ,具有反式尖晶石结构的Fe3O4 比刚玉型的α Fe2O3 更易与钾助催化剂发生相互作用 :α Fe2O3-K2O需经850℃煅烧才能生成多铁酸钾 ,但在Fe3O4 -K2O体系中只需700℃即可.而且 ,钾还可抑制Fe3O4 被氧化为α Fe2O3 的进程 ,在空气中 ,Fe3O4 只需300℃煅烧即可明显转化为α Fe2O3 ,但同样的转化在Fe3O4 K2O体系中要经700℃煅烧才会明显地发生.实验结果表明 ,某种形态的多铁酸钾可能是催化剂中的储钾相.

XRD Characterization of Interaction between Potassium Promoter and Magnetite

Interactions of the potassium promoter with different kinds of iron oxide as the active component of the catalyst for ethylbenzene dehydrogenation were investigated and compared with each other.By means of XRD method,it was found that magnetite in the form of the inverse spinel structure interacted easily with the potassium promoter to form potassium polyferrate in comparison to hematite with the corundum structure.In the Fe3O4-K2O system,the phase of potassium polyferrate could be formed at temperature of ～700℃,while for the α Fe2O3-K2O system,the temperature as high as ～850℃ was required for the formation of the potassium polyferrate phase.Moreover,incorporation of the potassium promoter into the magnetite(Fe3O4) would be in favor of inhibiting the oxidation of Fe3O4 to α-Fe2O3 in the process of calcination in air,as evidenced by the experimental fact that pure Fe3O4 could be converted into α-Fe2O3 by calcination in air at a temperature as low as ～300℃,whereas for the system of Fe3O4-K2O (10％),a calcination temperature not lower than ～700℃ was required for realizing this conversion.Thus,it could be suggested that the potassium polyferrate was probable to serve as a storage phase for potassium in the catalyst of ethylbenzene dehydrogenation to styrene.