Abstract

The fine crystal structure of hematite samples used for preparing potassium promoted iron oxide catalysts of dehydrogenation is studied via X-ray diffraction and scanning electron microscopy. α-Fe₂O₃ samples are synthesized under non-equilibrium conditions from several precursors in different regimes of thermolysis. The most important characteristic of hematite that causes the activity and selectivity of a hematite-based catalyst is its fine crystal structure (FCS). The fine crystal structure of hematite predetermines the phase composition of the catalyst. The fine crystal structure of hematite forms during its synthesis and is determined by the nature of the precursor, the temperature of synthesis, the temperature gradient, and the rate of the removal of gaseous thermolysis products. The highest activity is displayed by the catalyst prepared on the basis of hematite with mosaic blocks 70–90 nm in size and a minimum SF concentration caused by half and quaternary dislocations. Such hematite was synthesized via the thermolysis of iron sulfate at 950 K under fluidized bed and low temperature gradient conditions. Hematite from iron carbonate is not recommended for use in synthesizing a catalyst due to the high concentration of low-temperature SFs, which result in the formation of catalytically low-active potassium β-polyferrite.

中文翻译：

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前驱体和合成方式对赤铁矿制备促进氧化铁催化剂性能的影响

摘要

通过X射线衍射和扫描电子显微镜研究了用于制备钾促进的氧化铁脱氢催化剂的赤铁矿样品的精细晶体结构。α-Fe ₂ O ₃样品是在非平衡条件下由不同热解状态下的几种前体合成的。赤铁矿导致赤铁矿基催化剂的活性和选择性的最重要特征是其精细的晶体结构（FCS）。赤铁矿的精细晶体结构预先决定了催化剂的相组成。赤铁矿的精细晶体结构在其合成过程中形成，并由前体的性质、合成温度、温度梯度和气态热解产物的去除速率决定。以赤铁矿为基础制备的催化剂显示出最高的活性，其镶嵌块尺寸为70-90 nm，并且由半位错和四元位错引起的SF浓度最低。这种赤铁矿是通过硫酸铁在流化床和低温梯度条件下在950 K下热解合成的。不建议将碳酸铁赤铁矿用于合成催化剂，因为低温 SF 浓度高，会导致形成催化活性低的β-聚铁酸钾。