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

Abstract

The interaction between V₂O₅ and TiO₂ (anatase) was studied in the calcination temperature range of 500–850 °C. The activity of 1 wt% V₂O₅/TiO₂ calcined at 800 °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 °C, the vanadium supported on TiO₂ exhibited a loss in specific surface area, and the rutile phase appeared at 850 °C. The state of the supported vanadium phase, with varying VO_x surface densities, was found to depend on the calcination temperature. For calcination temperatures at 500, 600, and 800 °C, the NO_x 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 °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 °C. As the calcination temperature reached 850 °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.