Facet–Activity Relationship of TiO₂ in Fe₂O₃/TiO₂ Nanocatalysts for Selective Catalytic Reduction of NO with NH₃: <i>In Situ</i> DRIFTs and DFT Studies

Abstract

Anatase TiO2 nanosheets (TiO2-NS) and nanospindles (TiO2-NSP) have been successfully prepared with F– and glacial acetic acid as structure-directing agents, respectively. The Fe2O3/TiO2-NS and Fe2O3/TiO2-NSP nanocatalysts were prepared by a wet incipient impregnation method with a monolayer amount of Fe2O3. All the catalysts were employed for the selective catalytic reduction of NO with NH3 (NH3-SCR) in order to understand the morphology-dependent effects. It is interesting that the Fe2O3/TiO2-NS nanocatalyst exhibited better removal efficiency of NOx in the temperature range of 100–450 °C, which was attributed to more oxygen defects and active oxygen, acid sites, as well as adsorbed nitrate species based on Raman spectra, XPS, NH3-TPD, NO+O2-TPD, and in situ DRIFTS. The density functional theory (DFT) method was used to clarify the NO and NH3 adsorption abilities over the catalyst models of Fe2O3/TiO2{001} and Fe2O3/TiO2{101}. The results showed that the NH3 adsorption energy over the TiO2{001} (−2.00 eV) was lower than that over TiO2{101} (−1.21 eV), and the NO adsorption energy over TiO2{001} (−1.62 eV) was also lower than that over TiO2{101} (−0.29 eV), which agreed well with the experimental results that Fe2O3/TiO2-NS achieved higher catalytic activity than Fe2O3/TiO2-NSP for NH3-SCR of NO. In addition, the rapid electron transfer and regeneration of Fe3+ on the {001} facet of Fe2O3/TiO2-NS also promoted the NH3-SCR reaction efficiency. This work paves a way for understanding the facet–activity relationship of Fe2O3/TiO2 nanocatalysts in the NH3-SCR reaction.