Effects of mass transfer on Fischer-Tropsch kinetics over mesoporous silica-supported Co[sbnd]Mn[sbnd]Ce nano catalysts in a fixed-bed reactor

Abstract

An impregnated ternary mixed oxide (CoMnCe) on nano silica support was applied, as a novel Fischer-Tropsch catalyst, in a fixed-bed reactor. Using catalysts of various pellet sizes, the Thiele modulus was determined to quantify regions of pore diffusion resistance and surface reaction. Mechanistic studies were conducted via intrinsic kinetic experiments under no pore diffusion conditions (i.e. Thiele modulus<0.4) as follows: T = 483.15–583.15 k, P = 2–6 bar, H2/CO = 1–2, and GHSV = 4500 hr−1. Based on Langmuir–Hinshelwood–Hougen–Watson (LHHW) approach, the optimum mechanism was found to be associative adsorption of CO and H2 with the irreversible associative hydrogen, with the carbon monoxide adsorption determined as the rate-controlling step. For the optimum model, intrinsic activation energy, R-squared value, and mean absolute relative residual were obtained as 62 kj/mol, 0.97 and 10.41%, respectively. Finally, a promising graphical approach was proposed to predict effective reaction rate, considering the effects of internal mass transfer in catalyst beads.