Abstract
The oxidation of CO on silica-supported hematite (Fe2O3) was studied by the step−response method in a tubular fixed-bed reactor, at temperatures ranging between 270 and 350 °C. The oxidation process appeared to proceed through two stages. Firstly, oxygen atoms adsorbed on the surface of hematite react with gas phase CO according to an Eley−Rideal mechanism. Once that adsorbed oxygen has been consumed to some extent, surface oxygen from the lattice of iron oxide is removed in a second stage involving CO adsorption and CO reactive desorption steps, thus generating surface oxygen vacancies. Further reduction of hematite proceeds through diffusion of subsurface oxygen into surface oxygen vacancies. On this basis, a kinetic model was developed, which quantitatively describes the transient behavior of the oxidation process. The activation energies and pre-exponential factors of the rate constants and characteristic subsurface oxygen diffusion time could be determined.
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