MODELING CO OXIDATION ON SILICA-SUPPORTED IRON-OXIDE UNDER TRANSIENT CONDITIONS

The oxidation of CO on silica-supported hematite (Fe2O3) was studied b y the step-response method in a tubular fixed-bed reactor, at temperat ures ranging between 270 and 350 degrees C. The oxidation process appe ared to proceed through two stages. Firstly, oxygen atoms adsorbed on the surface of hematite react with gas phase CO according to an Eley-R ideal mechanism. Once that;adsorbed oxygen has been consumed to some e xtent, surface oxygen from the lattice of iron oxide is removed in a s econd stage involving CO adsorption and CO reactive desorption steps, thus generating surface oxygen vacancies. Further reduction of hematit e proceeds through diffusion of subsurface oxygen into surface oxygen vacancies. On this basis, a kinetic model was developed, which quantit atively 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 determin ed.