Geometric and electronic modification of the active Fe³⁺ sites of α-Fe₂O₃ for highly efficient toluene combustion

In the present study, catalytically inactive or low-active Ti⁴⁺ (d⁰) or Zn²⁺ (d¹⁰) ions were doped to α-Fe₂O₃ to tune the geometric and electronic engineering for Fe active center. X-ray absorption near edge structure (XANES) and Powder X-ray diffraction (XRD) analyses coupled with density functional theory (DFT) calculation show that the added of Ti⁴⁺ could occupy the interstitial octahedral or tetrahedral sites, resulting in surface Fe²⁺ species are oxidized to octahedrally coordinated Fe³⁺. As a result, more oxygen vacancies are generated, which improve the catalytic performance for toluene combustion. On the other hand, Fe²⁺ was substituted by Zn²⁺ ion could result in the partial destruction of hematite crystal structure, forming an additional phase of ZnFe₂O₄, and meanwhile part of Zn²⁺ ions replace the octahedrally coordinated Fe³⁺ sites, and therefore significantly decreasing the toluene catalytic performance. Moreover, our studies demonstrate that the combustions of toluene over Fe-based catalysts involve both the MvK and L-H mechanisms.