The Effect of Iron and Vanadium in VOy/Ce1-xFexO2-δ Catalysts in Low-Temperature Selective Catalytic Reduction of NOx by Ammonia

Supported VOy/Ce1-xFexO2-delta catalysts (x=0, 0.5, 0.1, 0.2) and bare supports were prepared and tested in selective catalytic reduction (SCR) of NOx by NH3 between 150 and 300 degrees C with a GHSV of 70 000 h(-1). Iron was found to be beneficial for the activity of the pristine supports, reaching 80 % conversion at 275 degrees C. When vanadium was additionally introduced into the system, iron was found to be detrimental for NOx-conversion. To derive structure-reactivity relationships, V-free supports and VOy/Ce1-xFexO2-delta catalysts were characterized by XRD, XPS, Raman spectroscopy and TEM. In situ XANES, as well as operando DRIFTS and EPR measurements were performed to study the behavior of the catalysts under reaction conditions. Up to an iron content of x=0.1, a solid Ce1-xFexO2-delta solution was formed. Higher iron contents led to formation of iron oxide agglomerates. These agglomerates, as well as an increased amount of surface oxygen species were found to be responsible for increased NOx-conversion over of pure supports. For V-containing catalysts, an interaction of Fe and V centers could be found. Under reaction conditions, Fe3+ was preferentially reduced instead of V5+, decreasing the catalytic activity of VOy/Ce1-xFexO2-delta.