Deactivation mechanism of commercial V₂O₅-WO₃-TiO₂ SCR catalysts used in 1 000 MW coal-fired power plant

The fresh and used catalyst( 25 000 h) samples which are both from selective catalytic reduction(SCR) equipment of a 1 000 MW coal-fired power plant were examined and characterized by means of scanning electron microscope (SEM) X-ray diffraction (XRD), brunauer, emmett and telle(BET), X-ray fluorescence (XRF), Fourier transform infra-red (XPS) and X-ray photoelectron spectroscopy (XPS), and the influencing factors causing catalyst deactivation were explored. The deNO_x activity (84%) at 375℃ and the specific surface area( 49 m²/g)of the fresh catalyst were a little more than those of the used catalyst (46%, 40 m²/g). The activity vanadium V⁵⁺ and surface chemisorbed oxygen O_α contents in the used catalyst were respectively increased from 46% and 24% to 56% and 34% compared to the fresh one, and large quantities of sulfates deposited on the surface as well as the volatilization of active ingredients was also found. Moreover, the results of SEM and XRD showed that the thermal sintering occurred on the surface of the used catalyst. Consequently, the V₂O₅-WO₃/TiO₂ catalyst deactivation could be attributed to the valence change of V and W atom, thermal sintering, impurities in deposit, and the decreasing of the specific surface area.