Thermal stability of vanadia-tungsta-titania catalysts in the SCR process

The thermal behaviour of TiO2-WO3-V2O5 catalysts with various vanadia contents (1, 2 and 3 wt.% V2O5) was investigated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and BET surface area determination. The activity and selectivity of the new and thermally treated catalysts were tested in the SCR reaction. Both structural and catalytic investigations have shown that the vanadia content has a strong effect on the thermal behaviour of the SCR catalysts. The structural investigations evidenced anatase sintering, increase of polymeric vanadyl surface species and three-dimensional growth of supported vanadia. upon ageing. The catalytic tests have shown that the SCR activity of catalysts containing 1 or 2% V2O5 increased upon ageing, whereas the SCR performance of the catalyst with 3% V2O5 decreased. The observed improvement of the SCR performance is attributed to an increase of the amount of polymeric vanadyl surface species upon ageing. The decrease of the SCR performance of the catalyst with 3% V2O5 is due to the extensive loss of surface area and to the three-dimensional growth of supported vanadia upon ageing. The catalyst containing 2% V2O5 represents the best compromise between high SCR activity and good thermal stability. (C) 2002 Elsevier Science B.V. All rights reserved.