Vanadia-based SCR catalysts supported on tungstated and sulfated zirconia: Influence of doping with potassium

A series of vanadium-based SCR catalysts supported on sulfated or tungstated ZrO2 were synthesized and characterized by means of N2-BET, XRD, NH3-TPD and in situ Raman spectroscopy. The effect of potassium doping on the properties of vanadia species was studied in detail. A number of catalyst preparation parameters were examined, including the choice of precipitant, variation of carrier surface area, potassium poisoning, crystallinity, and ZrO2-phase composition. The results show that the catalyst structure and SCR activity are affected from the synthesis route by the support crystallinity and morphology, the surface composition, and the molecular configuration of the dispersed vanadates. It was observed that poisoning with potassium had a negligible effect on the surface vanadate species (especially the VO stretching frequency observed by in situ Raman spectroscopy) if supported on the sulfated zirconia. Conversely, a more pronounced influence on the structure of surface vanadate was observed for the corresponding unsulfated samples, in which a significant red shift in the VO stretching frequency was observed on potassium doping. Computational studies suggested that potassium was responsible for both the observed decrease in VO stretching frequency and the higher proportion of dimers and higher polymers through coordination between K+ and two neighbouring VO. The results suggest an increased resistance toward potassium doping for the vanadia-based catalysts supported on sulfated zirconia.