Effect of gallium additions on reduction, carburization and Fischer-Tropsch activity of iron catalysts

Abstract

Undoped and gallium-doped iron oxide catalysts (100Fe, 100Fe:2Ga, and 100Fe:5Ga) were prepared by following a continuous co-precipitation technique using ammonium hydroxide as precipitant. The catalysts were characterized by BET surface area, X-ray diffraction, H-2-temperature programmed reduction, Fe-57 Mossbauer spectroscopy, and temperature programmed decarburization techniques. The addition of gallium affects both reduction as well as carburization of iron oxide. The CO conversion decreases with an increase of gallium content relative to iron. The gallium-doped iron catalyst (100Fe:2Ga) exhibits initially a lower CO conversion after H-2 activation than an undoped iron catalyst; however, the activity of the doped catalyst kept increasing with time. A strong interaction between iron oxide and gallium could explain the suppressed formation of chi-Fe5C2 and metallic iron during the carburization and reduction of iron oxide, respectively. The relative percentage of iron in chi-Fe5C2 was found to correlate with the initial rates of FT and WGS activity indicating that iron carbide is the main active component for both FT and WGS reactions.