La and Co Addition to Mn/TiO2 Catalysts for Enhancing Low-Temperature Denitrification Activity and H2O/SO2 Tolerance

Manganese oxide-based denitrification catalysts supported by anatase with active components of Mn, Mn–La, Mn–Co, and Mn–La–Co oxides were prepared by a coprecipitation approach, and comparisons of their catalytic activities were made. The influences of Co and La addition on the NO removal and H2O/SO2 tolerance of the MnOx catalysts were investigated. The reasons for the different catalytic performances were investigated by using XRD, XPS, H2-TPR, and NH3-TPD experiments. The reaction mechanism of selective catalytic reduction of NOx with ammonia was determined by in situ diffuse reflectance infrared Fourier transform spectroscopy. Experiments proved that the addition of Co and La expanded the active temperature window (120–369 °C) and improved the sulfur tolerance due to the increase in the contents of Mn4+ and surface-active oxygen, along with the enhancement of the redox capacity of the catalyst. Different NH3–SCR reaction mechanisms were found over the catalysts Mn–La–Co/TiO2 and Mn/TiO2: the former was both the Eley–Rideal and Langmuir–Hinshelwood mechanisms, while the latter followed only the Langmuir–Hinshelwood mechanism. In addition, a "fast SCR" reaction mechanism was active for all catalysts. This work provides useful insights for improving the sulfur tolerance of manganese-based denitrification catalysts.