The Role of CeO2 as a Gateway for Oxygen Storage over CeO2-Grafted Fe2O3 Composite Materials

The surface grafting of CeO2 onto Fe2O3 with a 1:5 molar ratio produced a thermally stable composite material with greater and faster oxygen storage/release than its separate constituents. In the composite, CeO2 and Fe2O3 were intimately contacted by interfacial Ce-O-Fe bonding, and no solid solutions or mixed Ce and Fe oxides were formed after heating at 900 degrees C. The oxygen storage capacity and initial rate of oxygen release/storage were both increased in the composite structure by virtue of the Fe2O3 and CeO2, respectively. The reduction oxidation cycles in which Fe2O3 is reduced via Fe3O4 to Fe metal by CO or H-2 and then reoxidized by O-2 were stabilized by surface-grafting Fe2O3 with CeO2. In situ Raman spectra demonstrated that the surface-grafted CeO2 acts as an oxygen gateway, activating the dissociation of O-2 into oxide ions or the recombination of oxide ions into O-2 and transferring oxide ions to/from Fe2O3. Meanwhile, Fe2O3 acts as an oxygen reservoir that expands the O-2 storage capacity. The composite material was tested in a simulated exhaust gas stream with lean/rich perturbations (which occur in automotive three-way catalysts). The synergistic effect of the surface grafting effectively buffered the system against air-to-fuel ratio fluctuations.