Effect of the Precursor and Synthesis Mode on the Properties of Hematite for the Preparation of Promoted Iron Oxide Catalysts

Abstract

The fine crystal structure of hematite samples used to prepare potassium-promoted iron oxide dehydrogenation catalysts has been studied by X-ray diffraction and scanning electron microscopy. Samples of α-Fe2O3 were obtained under nonequilibrium conditions from several precursors under different thermolysis regimes. The most important characteristic of hematite, which determines the activity and selectivity of the catalyst based on it, is the fine crystal structure (TCS). The TCS of hematite determines the phase composition of the catalyst. The TCS of hematite is formed during the synthesis of hematite and is determined by the nature of the precursor, the temperature of sample synthesis, and the temperature gradient of the rate of removal of gaseous thermolysis products. The highest activity was demonstrated by a catalyst prepared on the basis of hematite with mosaic blocks of 70–90 nm, with a minimum concentration of SF due to half and quaternary dislocations. Such hematite was obtained by thermolysis of iron sulfate at 950 K under fluidized bed conditions and a low temperature gradient. Hematite from iron carbonate is not recommended for the synthesis of a catalyst due to the high concentration of low-temperature SF, which leads to the formation of catalytically inactive potassium β-polyferrite.