MnO2–GO-scroll–TiO2–ITQ2 as a low-temperature NH3-SCR catalyst with a wide SO2-tolerance temperature range

Abstract

Three steps are needed to improve the steam-resistance and SO₂-resistance of a catalyst for the selective catalytic reduction of NO_x through NH₃ at low temperature: the first is to introduce a protective layer to reduce the direct contact between SO₃ and the catalyst. Then, there is delayed oxidation, which fundamentally reduces the oxidation of SO₂ to SO₃. If the catalyst is used at a relatively high temperature, it will inevitably produce SO₃. The third step is to add a strong acid site in addition to reducing the acidity of the catalyst, which first absorbs NH₃ and then absorbs SO₃, to seize NH₄HSO₄, so that it does not cover the active site. GO was used to curl and wrap around the outside of MnO₂ nanowires as a protective layer. TiO₂ was selectively deposited on oxygen-containing functional groups on GO, which delayed the oxidation ability of the catalyst. ITQ2 molecular sieves acted as strong acid sites to absorb NH₄HSO₄. The curling behavior of GO outside MnO₂ nanowires, the deposition location of TiO₂ and the distribution of ITQ2 were explained by morphology and elemental analysis. In the range of 150 °C to 280 °C, the MnO₂–GO-scroll–TiO₂–ITQ2 catalyst conversion of NO to N₂ was more than 85%. Combined with H₂-TPR and activity testing, the source of the wide SO₂-tolerance temperature range of the catalyst was described in detail.