Preparation of ultrafine Fe-Si-C powders in a radio-frequency thermal plasma and their catalytic properties

Ultrafine Fe-Si-C powders were prepared from mixed gases of SiH₄-CH₄-Fe(CO)₅ using a newly developed thermal-plasma apparatus with a dual-radio-frequency-coupled-plasma-torch system. The phases of the powders prepared were classified into two groups; one composed of -FeSi₂ which was prepared by rapid quenching, while the other was composed of -Fe, Fe₃Si, Fe₅Si₃, FeSi, -SiC and amorphous Si, which were prepared by slow quenching. The diameters of these powders were in the range 5–50 nm. The catalytic activities of these powders for Fischer-Tropsch synthesis were examined. The ultrafine -FeSi₂ powder was very active for the selective formation of olefin. On the other hand, powders of -Fe, Fe₃Si and Fe₅Si₃ were low in their selectivity but gave high CO conversion. Relations between the plasma conditions for the preparation of ultrafine Fe-Si-C powders and their catalytic properties are discussed.