N₂O inhibition by toluene over Mn-Fe spinel SCR catalyst

Co-removal of toluene in NH₃-SCR unit over Mn based catalysts is desirable but still faces the big challenge of byproduct greenhouse gas N₂O. In this work, the impacts of toluene on N₂O formation mechanism was studied. The main N₂O formation pathways in NH₃-SCR over Mn-Fe spinel were NH₃ oxidation and non-catalytic selective reduction (NSCR), in which NSCR dominated below 250 °C. The N₂O from NSCR through both Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanisms was confirmed. And the E-R mechanism was dominant at 200 °C. Toluene was effectively co-removed with NO_x with the advantage of N₂O inhibition. Toluene suppressed N₂O generation from both NH₃ oxidation and NSCR. NH₃ oxidation by gaseous O₂ and catalyst surface oxygen was all limited by toluene, resulting in less adsorbed NH that was further proved by the larger energy barriers of NH₃*→NH₂* and NH₂*→NH* on toluene pre-adsorbed catalyst surface. NO oxidation was also limited, suppressing the generation of adsorbed NO₃^-. Due to the inhibition of NH₃ and NO activation to key intermediates NH and NO₃^-, respectively, the N₂O generation from E-R route was slightly decreased in the presence of toluene, while that from L-H route was completely prohibited at 200 °C.