Insight into the promotional effect of NO2 on toluene oxidation over MnCe/HZSM-5 catalyst

A thorough probe into the activation mechanism of NO2 on toluene oxidation during co-removal of toluene in NH3-SCR unit is imperative but still lacking. This study unraveled the promotional effects of NO2 on toluene conversion, CO2 selectivity and catalytic stability over a MnCe/HZSM-5 catalyst. 1000 ppm NO2 was sufficient for complete oxidation of 50 ppm toluene into CO2 at 280 °C in the absence of O2 (C7H8 + 18NO2 → 7CO2 + 4H2O + 18NO). NO2 had stronger oxidizing ability than O2, while O2 re-oxidized NO to NO2, resulting in a synergistic contribution to toluene conversion. NO2 participated in toluene oxidation producing predominant NO and negligible organic N-byproducts. The N in NO2 scarcely took part in the organic synthesis process. NO2 gave one of its O easily to provide additional Osur and improved mobility and activity of Olat, hence speeding up the re-oxidation of reduced metal sites. The activation of NO2 on toluene oxidation predominantly followed Mars-van Krevelen mechanism. The Langmuir-Hinshelwood mechanism also existed but was less important.