CHARACTERIZATION OF PROMOTED MAGNETITE USING ANALYTICAL ELECTRON-MICROSCOPY TECHNIQUES

The microstructures of fused iron catalysts in the unreduced and parti ally reduced state have been investigated using analytical electron mi croscopy techniques. In the unreduced state, B '''-potassium ferrites of 0.1 to 0.3 mu m in size were found to precipitate uniformly and sem i-coherently at the centers of the magnetite dendrites. These precipit ates were identified as K2O . 4FeO . 15Fe(2)O(3) potassium ferrites, h aving lattice fringes of ca. 1.72 nm, which corresponded to the distan ce between the [KO](-) planes. During hydrogen reduction, a well delin eated porous structure develops which can be described by the (0001)K2 O . 4FeO . 15Fe(2)O(3) parallel to (($) over bar 111)Fe3O4 (($) over b ar 110)Fe parallel to Pore Channel and the (2 ($) over bar 1 ($) over bar 10)K2O . 4FeO . 15Fe(2)O(3) parallel to (0 ($) over bar 22)Fe3O4 p arallel to (002)Fe perpendicular to Pore Channel, crystallographic ori entation relationship. This indicates that the potassium ferrite preci pitates, which are still present in the partially reduced structure, h ave their potassium conduction bands parallel to the pore channels. It was concluded that the presence of these uniformly distributed B '''- potassium ferrites and their orientation relationship with the pore ch annels are responsible for the high atomic surface coverage of potassi um obtained in the catalyst.