MnO2–Graphene-oxide-scroll–TiO2 composite catalyst for low-temperature NH3-SCR of NO with good steam and SO2 resistance obtained by low-temperature carbon-coating and selective atomic layer deposition

Abstract

The improvement of the steam and SO₂ resistance of low-temperature selective catalytic reduction of NO_x by an NH₃ (NH₃-SCR) reaction catalyst requires two steps: first, carbon-coating at low temperature and then the stabilization of the carbon layer. A low-temperature carbon-coating method was established and illustrated by using graphene oxide (GO) sheets to crimp and wind around the outer surface of MnO₂ nanowires. The TiO₂ was selectively deposited on the oxygen-containing functional groups of GO by atomic layer deposition to provide a method for protecting the carbon layer. The morphology (TEM) and element analysis (STEM) results revealed that the scrolling of GO on the outside of MnO₂ and then the deposition of TiO₂ on GO had led to the formation of MnO₂–graphene-oxide-scroll–TiO₂ composites (MnO₂–GOS–TiO₂). Coupling H₂-TPR, DRIFT and activity test results with DFT, it was discovered that the electron-induced effect between the GO, MnO₂ and TiO₂ neutralizes the enhanced activity after the combination of GO and MnO₂ and the decreased activity after the combination of TiO₂ and MnO₂, which gives the composited structure a conversion of more than 84% to N₂ in the range of 150 °C to 280 °C. Meanwhile, the GOS–TiO₂ layer was shown to boost the catalytic stability remarkably in an environment containing steam and SO₂ due to a shielding effect from SO₂ and delayed oxidation. The synergistic effect of GO and TiO₂ thus improved the steam and SO₂ resistance of the manganese-based catalyst at low temperature.