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

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 NOx 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. NOx on TiO2NP 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.