Low-temperature synthesis of nanostructured χ-Fe5C2 platelets in CO + H2 atmospheres

Nanosize platelets of χ-Fe5C2 were produced as a by-product of the Fisher-Tropsch reaction during the synthesis of gasoline. Gas mixtures of CO and H2 were used at 593 K and 2.1 MPa over an α-Fe porous aggregate catalyst. The porous α-Fe catalyst consisted of 30–50 nm sized nanocrystallites held together by an alumina rich region. When the catalyst was exposed to the CO + H2 gas mixture, the α-Fe crystallites formed equiaxial clusters 100 to 300 nm in size and carbon deposition took place homogeneously around these clusters until all the pores were filled. Further carbon deposition resulted in the disintegration of the catalyst. The clusters were found isolated, detached from similar clusters and completely surrounded of carbonaceous material. After 320 h of exposure to the gas mixture, the α-iron clusters transformed into χ-Fe5C2 platelets of width 100 to 300 nm and thickness 30–50 nm.