Topotactixity of the hydrogen reduction process in fused iron catalyst

Microstructural characterization of highly porous fused iron catalyst in the reduced and partially reduced states has been performed using electron microscopy techniques. The microstructure consists of 30–50nm iron crystallites in a network of highly defected iron, forming an interconnected porous structure. The size of the pores ranges from 10 to 20nm and they are aligned along a specific crystallographic direction of magnetite and/or iron. We found that the {111}Fe3O4 and the {011}Fe planes are preferentially reduced and preferentially exposed, respectively, during reduction. The magnetite-α-iron-pore channel chrystallographic orientation relationship can be expressed as (1̄11)Fe3O4 // (1̄10)Fe // pore channel and (02̄2)Fe3O4 // (002)Fe ⊥ pore channel. The former is known as the Nishiyama-Wassermann orientation relationship between face-centered and body-centered cubic materials. It is suggested that the high activity of this catalyst is due to the presence of alkali atoms on top of every other closely packed iron atom.