Reduction of Iron Oxide Catalysts: The Investigation of Kinetic Parameters Using Rate Perturbation and Linear Heating Thermoanalytical Techniques

Abstract

The mechanisms and kinetics of the reduction of powdered Fe 2 O 3 and Fe 3 O 4 samples have been investigated under nonisothermal conditions to provide a detailed insight into the processes occurring. Both conventional linear heating temperature-programmed reduction (TPR) and constant rate temperature-programmed reduction (CR-TPR) techniques were utilized. Fe 2 O 3 was found to reduce to Fe in a two-step process via Fe 3 O 4 . The mechanism of the prereduction step of Fe 2 O 3 to Fe 3 O 4 was found to follow an n th order expression where nucleation or diffusion was not the rate-controlling factor while the main reduction step to metal was described by a model involving the random formation and growth of nuclei. A CR-TPR rate perturbation method, “rate-jump”, was applied to the measurement of variations in apparent activation energy throughout the reduction processes, under near-equilibrium conditions and the activation energy measurements are compared with those obtained under conventional linear heating conditions.