MW燃煤电厂钒钛系脱硝催化剂失活原因分析

以某燃煤电厂1 000 MW发电机组选择性催化还原（SCR）装置使用前和运行25 000 h后的烟气脱硝催化剂为研究对象,对催化剂进行脱硝活性测试,同时应用扫描电镜（SEM）、X射线衍射（XRD）分析、比表面积和孔容（BET）分析、X射线荧光光谱（XRF）分析、傅里叶红外（FT-IR）和X射线光电子能谱（XPS）分析进行表征分析,探讨催化剂失活机制.结果表明： 活性检测375 ℃下运行后催化剂的脱硝效率（46%）和比表面积（40 m2/g）相对于新鲜催化剂（84%,49 m2/g）都有所下降,同时表面的活性钒V5+和化学吸附氧Oα由56%和34%分别下降至46 %和24%,并且有大量盐类沉积及少量活性组分的损失,SEM和XRD的结果表明运行后催化剂表面存在严重烧结现象.因此,催化剂表面的烧结、还原能力的下降、盐类沉积以及活性组分的挥发都与催化剂活性下降有关.

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 deNOx 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 Oα 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.