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 is 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 catalysts structure and SCR activity is affected from the synthesis route by means of 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 V=O 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, where a significant red shift in V=O stretching frequency was observed upon potassium doping. Computational studies suggests that potassium is responsible for both the observed decrease in V=O stretching frequency and the higher proportion of dimers and higher polymers through coordination between K+ and two neighbouring V=O.

The results suggest an increased resistance towards potassium doping for the vanadia-based catalysts supported on sulfated zirconia.