The effect of calcination temperature on the structure and activity relationship of V/Ti catalysts for NH3-SCR

The interaction between V2O5 and TiO2 (anatase) was studied in the calcination temperature range of 500-850 degrees C. The activity of 1 wt% V2O5/TiO2 calcined at 800 degrees C was found to be comparable to that of the 1 wt% V2O5-10 wt% WO3/TiO2 catalyst. The V2O5/TiO2 series catalysts were characterized by BET, XRD, XRF, HRTEM, in situ Raman spectroscopy, in situ DRIFTS, H2-TPR, and XPS. As the calcination temperatures were increased from 500 to 850 degrees C, the vanadium supported on TiO2 exhibited a loss in specific surface area, and the rutile phase appeared at 850 degrees C. The state of the supported vanadium phase, with varying VOx surface densities, was found to depend on the calcination temperature. For calcination temperatures at 500, 600, and 800 degrees C, the NOx conversion of V2O5/TiO2 catalysts increased with temperature. This was related to the rise of the polymeric vanadyl species and the higher redox capacity per unit specific surface area. However, at 700 degrees C, the NH3-SCR activity decreased, resulting from the decrease of polymeric vanadyl and the per unit specific surface area redox capacity. Additionally, there was an increase in specific surface acid sites and monomeric vanadyl species at 700 degrees C. As the calcination temperature reached 850 degrees C, the formation of rutile and the reduction in the redox capacity per unit specific surface area led to a decline of NH3-SCR activity.