Redox Characteristics of O 2 and NO 2 in the Fast NH 3 -Selective Catalytic Reduction of NOx Over Vanadium-Based Catalyst

The redox property of catalysts in response to oxygen is one of the most important factors in selective catalytic reduction (SCR) reactions. In particular, the capacity to reoxidize V in V/TiO2 catalysts determines the reaction activity at low temperatures. Fast SCR reactions do not involve oxygen at an NO2/NOx = 0.5 but they show remarkable activity (near 100%). In a fast SCR reaction, the reoxidation of the catalyst is possible not only by oxygen but also by NO2. In this study, we showed that a catalyst reduced by ammonia was reoxidized and produced NO through a reaction with NO2 and was faster than reoxidation by O2 according to NO2 on/off experiments. X-ray photoelectron spectroscopy (XPS) analysis of the valence of the catalyst showed that the reoxidation of V+4-OH to V+5 = O by the SCR reaction varied. The present study demonstrated that NO2 was superior to O2 for low-temperature SCR reactions, though the approach was different from the existing reports.