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

Nitrogen oxides (NOx) 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 NOx 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 NOx and CH3SH. In the absence of CaO, the SO42– species generated from the oxidation of CH3SH can occupy CuO sites, resulting in suboptimal CO2 selectivity. However, in the presence of CaO, the SO42– 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 NOx and CH3SH. This research offers valuable insights for designing catalysts capable of synergistically eliminating NOx and sulfur-containing VOCs in complex flue gases containing alkaline impurities.