On the kinetics and mechanism of Fischer Tropsch synthesis on a highly active iron catalyst supported on silica-stabilized alumina

The kinetics of a supported iron Fischer-Tropsch (FT) catalysts were investigated and a physically meaningful model that fits the data very well is proposed. Kinetic data (reported herein) were obtained at 250 degrees C and 20 atm in a fixed bed reactor at a variety of P-H2 and P-CO. Measured P-H2 and P-CO power law dependencies were found to be in the same range as those for unsupported Fe FT catalysts previously reported. The kinetic models in this study were tested using a statistical lack-of-fit test. Eight, two-parameter Langmuir-Hinshelwood rate expressions based on various mechanistic routes and assumptions were derived and tested, but all gave relatively poor fits to the data. An adjustment of the P-H2 dependency of the derived expressions to the 0.875 power resulted in three reasonable semi-empirical models, one of which fit the data extremely well. This approach also allowed us to determine the best function of P-CO dependency. The results suggest that supported Fe FT catalysts follow a direct CO dissociation pathway, that carbon is one of the most abundant species on the surface of the catalyst, and that the hydrogenation of either C* or CH* is the rate-determining step. (C) 2015 Elsevier B.V. All rights reserved.