EFFECTS OF PREPARATION ON THE PROPERTIES OF MO, AL, AND CA PROMOTED FE/MGO CATALYSTS

The texture, morphology, and state of iron in the Fe/MgO catalyst with Mo, Al, and Ca promoters have been investigated. It was established that a new Fe-containing phase appeared in all promoted samples after calcination at 723 K, which might be attributed to MgFe2O4. After reduction in hydrogen at 603 K, the phases identified by XRD were MgO and α-iron in all cases except for the aluminum promoted sample. Mössbauer investigation of this latter sample revealed that most of the iron remained in the Fe3+ state and only a small part of it was reduced to Fe2+. The limited reduction is attributed to the prevailing presence of spinel-type oxides. Different preparation conditions (drying in air or in vacuum) resulted in morphological changes; smaller iron particles are formed upon reduction of samples dried in vacuum. Comparison of the size of the metal particles and that of the support shows that the characteristic size of iron considerably exceeds the size of the grains of the support. © 1992.