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

Abstract

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.