Synergistic Catalytic Elimination of NO_x and CH₃SH in CaO-Containing Flue Gases

Nitrogen oxides (NO_x) and methyl mercaptan (CH₃SH) are prevalent atmospheric pollutants that frequently coexist in industrial flue gases emitted from the petroleum chemical industry, municipal waste incineration, and biomass combustion. It is challenging to achieve the synergistic catalytic elimination of NO_x and CH₃SH in CaO-containing flue gases. A comprehensive investigation into the copoisoning mechanisms of CaO and CH₃SH is essential yet remains insufficiently explored. In this work, we unravel the antagonistic effects between CaO and sulfate species on a CuO/Al₂O₃ model catalyst during the synergistic catalytic elimination of NO_x and CH₃SH. In the absence of CaO, the SO₄^2- species generated from the oxidation of CH₃SH can occupy CuO sites, resulting in suboptimal CO₂ selectivity. However, in the presence of CaO, the SO₄^2- species can preferentially bind to CaO that is combined with the Al₂O₃ support. Such a CaO-induced shift in sulfate species bridging behavior not only liberates CuO active sites but also modulates their electronic structures, thereby enhancing the CO₂ selectivity. These findings demonstrate that CaO can mitigate the poisoning effects of CH₃SH on the catalyst during the synergistic catalytic elimination of NO_x and CH₃SH. This research offers valuable insights for designing catalysts capable of synergistically eliminating NO_x and sulfur-containing VOCs in complex flue gases containing alkaline impurities.