Enhancement of low temperature NH3-SCR activity and SO2 & H2O tolerance over VPO-Co/TiO2: Determining roles of acidity via Co doping

A series of VPO-Co/TiO2 samples were synthesized for selective catalytic reduction of NOx with NH3 (NH3-SCR) at low temperature for the first time. The activity testing results suggested that the catalytic performance of VPO-Co/TiO2 was greatly improved after Co was introduced. Among all the catalysts, VPO-Co(0.07)/TiO2 provided the optimal low-temperature SCR activity, with NO conversion 100% and N2 selectivity above 98% at 180–270 °C. Additionally, VPO-Co(0.07)/TiO2 also presented extraordinary SO2 + H2O durability after introducing 200 ppm SO2 and 6 vol% H2O to the SCR reaction at 180 °C. The characterization results revealed that the oxidation capacity and the acidity were both improved with the Co doping. In this VPO-Co/TiO2 system, the increased acidity via the Co doping played a more critical role in raising the SCR activity. The richest surface acidity could offset the adverse effect of moderate oxidation capacity over VPO-Co(0.07)/TiO2, thus resulting in the best de-NOx performance at low temperature. Furthermore, the in-situ diffuse reflectance Fourier transform infrared spectroscopy (in-situ DRIFTS) studies revealed that the SCR reaction over VPO-Co(0.07)/TiO2 was proceeded via a combination of Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) pathways at 180 °C.