Promotional effect of the TiO2 (001) facet in the selective catalytic reduction of NO with NH3: in situ DRIFTS and DFT studies

Abstract

Surface engineering of TiO₂ is significant in the SCR reaction and worth studying. In a previous study, we found that TiO₂ nanosheets (TiO₂-NS) with the (001) plane exhibited a much better SCR performance than TiO₂ nanoparticles (TiO₂-NP) with the (101) plane. In this work, in situ DRIFTS and DFT calculations were applied to address the promotional effect of the (001) plane of TiO₂-NS in the SCR reaction. The behavior of adsorption and desorption of NO_x and NH₃ on the two surfaces was studied. It was found that NH₃ adsorbed on both TiO₂-NS and TiO₂-NP was in the form of NH₃(g) on the Lewis acid sites. NO_x on TiO₂-NP were mainly trans-(NO)₂ and N₂O₄ which were non-reactive. Differently, NO on TiO₂-NS was mainly in the form of NO₂ which was probably due to the high energy and abundant active oxygen species of the (001) facet. The formed NO₂ could trigger the subsequent ‘fast SCR’ reaction thereafter promoting the activity. Therefore, TiO₂-NS with more (001) facets had better SCR activity than TiO₂-NP with the exposed (101) facet.