The textural promotion of metallic iron by alumina

Textural promotion of iron catalysts, i.e., maintenance of high specific areas of reduced iron samples, is achieved by dissolved Al2O3 into Fe3O4 prior to reduction. A 10.2 wt% A12O3 in Fe3O4 sample with a known surface composition in the reduced state was investigated to determine the mode of textural promotion of reduced iron by alumina. The amount of Fe2+ inside the reduced iron crystallites was determined to be approx 1 wt% by Mössbauer effect spectroscopy. X-Ray line broadening indicated a 61 ± 3-nm crystal size in agreement with the BET particle size of the same sample. The paracrystallinity following Hosemann was determined to be 0.6, a value in agreement with an empirical correlation between particle size and paracrystallinity. All data presented here are compatible with Hosemann's view that molecular inclusions of FeAl2O4 in the iron lattice are responsible for textural promotion. Since particle size is inversely proportional to specific surface area, paracrystallinity may be a dominant cause of textural promotion in our case. Another cause may be a patchy monolayer of alumina at the surface of the iron particles, preventing sintering by a “skin” effect.