Synergistic Effect of Fe–Co Bimetallic Catalyst on FTS and WGS Activity in the Fischer–Tropsch Process: A Kinetic Study

The kinetics of Fischer–Tropsch (FT) and water–gas shift (WGS) reactions were investigated through detailed experimentation over a laboratory prepared 10Fe/20Co/SiO₂ catalyst. An investigation was undertaken to understand the prevailing mechanism of CO activation over a Fe–Co bimetallic catalyst. The mechanisms of CO adsorption and intermediate formation are different over an iron and cobalt catalyst, which finally affect the rate of CO consumption. The mechanism of CO consumption in the FT and WGS reactions over this catalyst has been studied in the light of the synergistic effect due to the presence of both Fe and Co phases. These different phase formations (active sites) were investigated using characterization techniques, namely, XRD, TEM, and SAED. The reaction kinetic study was performed at industrial relevant reaction conditions (T = 473–553 K, P = 1–3 MPa, GHSV = 1800–6600 mL/gcat-h, H₂/CO molar ratio = 0.5–2.5) in a continuous fixed bed reactor. The models based on rate of CO consumption were derived using the Langmuir–Hinshelwood–Hougen–Watson (LHHW) and Eley–Riedel (ER) approach. Mechanistic models were based on carbide, enol, and carbide plus enol mechanisms, where both H₂-assisted and -unassisted adsorption of CO were taken into consideration for the derivation. The selected models were validated with experimental data. Models based on the enol and carbide mechanisms were able to predict the rate of consumption of CO very well where the dissociation of CO was hydrogen assisted. Literature models were tested for the WGS reaction, and models based on formate mechanism fit the experimental data well.