Selective catalytic reduction of NOx by NH3 at low temperature over manganese oxide catalysts supported on titanate nanotubes

Abstract

We report the NO conversion with NH3 at low temperature over MnOx-supported on titanate nanotubes. The effect of SO2 and water on catalytic activity was also analyzed. For the catalytic activity tests, three catalysts with 1, 3, and 5 wt.% of MnOx were synthesized. A high NO conversion (92%) at 180 °C is reported for the 1Mn/NTiO2 catalyst. The further addition of MnOx to the support improves the catalytic activity but NO conversion (95%) was shifted to a higher temperature (from 180 to 220 °C). However, the presence of SO2 (50 ppm) and water (5 vol.%) diminishes the NO conversion up to 60%, which remains after 300 min. We found that addition of MnOx increases the Lewis acid sites concentration of the nanotubes. As the Lewis acid sites increase (from 1.86 to 3.56 µmol m−2), the Mn4+/Mn3+ ratio on the surface of the nanotubes decreases (from 4 to 1.6), which indicates that the surface of the catalysts is deficient in electrons. We concluded that a high Lewis acid sites concentration and a low Mn4+/Mn3+ ratio, hence a surface deficient in electrons, improves the catalytic activity to remove NO on the Mn/NTiO2 catalysts.