Structural images of the classical fused iron catalysts

1 Structural images of the classical fused iron catalysts 

There are two types of interspace present amongst the cube Octahedral interspace (B site) and tetrahedral interspace (A site), as shown in Fig. 3.62. The 32 of oxygen ions constitute the interspace of both 64 tetrahedrons and 32 octahedrons. In a crystal of Fe304, eight Fe + and eight Fe + ions occupy the octahedral interspace, while the another eight Fe + ions occupy the tetrahedral interspace, namely, Fe3+ (Fe2+ Fe3+) O4. 

What kind of metal ions can fill into the vacant interspace or replace Fe +, Fe + ions According to the principles of crystallography, the total amount of the chemical valences of several metal ions is equal to eight which makes the equilibrium of total chemical valences with four of oxygen ions. Various kinds of the metal ions can occupy A site or B site, respectively. The ionic distributions of which can be expressed by the following formulas  

The structure of ammonia synthesis catalyst used in industry comprises promoters that are uniformly distributed into the inner or on the sm-face of iron oxide precursor. The crystallites are very small so the reduced catalysts show the stable structures and the largest surface areas. 

Structural images of Fex — O based fused iron catalysts 

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