Redox Characteristics of O2 and NO2 in the Fast NH3-Selective Catalytic Reduction of NOx Over Vanadium-Based Catalyst

Abstract

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.