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

摘要

The mechanisms and kinetics of the reduction of powdered Fe_2O_3 and Fe_3O_4 samples have been investigated under nonisothermal conditions of provide a detailed insight into the processess occurring. Both conventional linear heating temperature-programmed reduction (TPR) and constant rate temperature-programmed reduction (CR-TPR) techniques were utilized. Fe_2O_3 was found to reduce to Fe in a two-step process via Fe_3O_4. The mechanism of the prereduction step of Fe_2O_3 to Fe_3O_4 was found to follow an nth order expression where nucleation or diffusion was not the rate-controlling factor while the main reduction step to metal was described by a novel 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.