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 NOx 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.