Studies with a precipitated iron Fischer-Tropsch catalyst reduced by H2 or CO

A precipitated Fe2O3 catalyst precursor was reduced by H-2 or CO and characterized by diffuse reflectance FT-IR with high-pressure syngas adsorption, syngas temperature-programmed desorption (TPD), XRD and BET surface area, and tested for FT synthesis from high-pressure syngas. The results show that on the H-2-reduced sample metallic iron particles are formed and on the CO-reduced sample a mixture of metallic iron and iron carbides are formed. The iron carbides on the CO-reduced sample can be decomposed to metallic iron by H-2 treatment at 300degreesC, and the metallic iron on the H-2-reduced sample can be partly converted to iron carbides by CO treatment at 300degreesC. Both the metallic iron and iron carbides on the reduced samples have high ability for CO dissociation. The BET surface area of the CO-reduced sample is about five times higher than that of the H-2-reduced sample. The treatment of the CO-reduced sample with H-2 and the treatment of the H-2-reduced sample with CO result in only small changes in the surface areas. During performing high-pressure FT synthesis, amorphous carbon-rich iron carbides and crystalline magnetite are formed, which have relatively weaker ability for CO dissociation than those of metallic iron and iron carbide particles on the freshly reduced samples. CO-reduced sample exhibits remarkably higher catalytic activity for FT synthesis than the H-2-reduced sample. Treatment of the CO-reduced sample with H-2 leads to an obvious decrease in the catalytic activity of the sample, and treatment of the H2-reduced sample with CO leads to a great increase in the activity. These results clearly indicate that those iron carbides formed during CO reduction of the precipitated Fe2O3 sample or CO treatment of the H-2-reduced sample have played an important role in enhancing the catalytic activities of the samples. (C) 2002 Elsevier Science B.V. All rights reserved.