烟气脱硝催化剂中载体TiO_2对催化性能的影响

Influence of TiO_2 -Supports on the Catalytic Properties of Catalyts for De-NO_x in Flue Gas

选用纳米级TiO2和工业级TiO2作为烟气脱硝催化剂的载体,采用分步浸渍法在载体TiO2上负载WO3和V2O5,得到商业催化剂的活性成分1%V2O5-10%WO3/TiO2,用以去除烟道气中的氮氧化合物(NOx)。纳米级催化剂所允许的空速范围远比工业级催化剂高,氨氮比(≥1.0)对纳米级催化剂脱硝效率基本没有影响,且当氨氮比为1.2时,在300～350℃脱硝效率可以达到100%。而工业级催化剂的脱硝效率随着空速的增加和氨氮比的降低而显著减小。在相同的空速(7500h-1)和氨氮比(1.0)条件下,纳米级催化剂的脱硝效率几乎为100%,而工业级催化剂只有在400℃时达到最大脱硝效率,且仅为85%。此外,以纳米级TiO2为载体的催化剂具有更宽的脱硝温度窗。利用扫描电镜(SEM)、N2物理吸附脱附、X射线衍射(XRD),程序升温脱附(NH3-TPD)和粒径分析等方法进行载体和催化剂表征。结果表明,纳米级催化剂的比表面积,孔容和表面酸性都远大于工业级催化剂。

Nano-TiO2 and industrial grade-TiO2 were selected and used as supports of catalysts for De-NOx in flue gas. V205 and WO3 were impregnated onto supports TiO2 to obtain the active components 1%V2O5-10%WO3/TiO2 of the commercial catalysts, which were used for the removal of NOx in flue gas. The allowed gas hourly space velocity（GHSV） of the catalyst supported on nano-TiO2 is much higher than that of the catalyst supported on industrial grade-TiO2. The NH3/NO molar ratio（≥1.0） almost has no effect on the NOx conversion of catalyst supported on nano-TiO2, and a complete conversion of NOx can be achieved with the NH3/NO molar ratio=1.2 in the range of 300-350℃. While the NOx conversion of the catalyst supported on industrial grade-TiO2 reduces significantly with the GHSV increase or the NH3/NO molar ratio decrease. Under the same GHSV（7500 h^-1） and NH3/NO molar ratio （1.0）, the NOx conversion of catalyst supported on nano-TiO2 reaches almost 100%, while the maximum NOx conversion of catalyst supported on industrial grade-TiO2 is only 85% at 400℃. Besides, the catalyst supported on nano-TiO2 has broader De-NOx temperature window. The supports and catalysts were characterized by scanning electron microscope （SEM）, N2 adsorption/desorption, X-ray diffraction （XRD）, temperature-programmed desorption for ammonia（NH3-TPD）, and particle size analysis The results show that the specific surface area, pore volume and surface acidity of the catalyst supported on nano-TiO2 are far larger than those of the catalyst supported on industrial grade-TiO2.