xCeO2-yWO3-TiO2脱硝催化剂抗SO2性能研究

Preparation and Properties of xCeO-yWO-TiO Denitrification Catalyst

目前中国面临着大气污染物氮氧化物排放限制要求,以及进一步提高商业催化剂(V2O5-WO3/TiO2)危废处理困难等问题,本文以工业偏钛酸为钛源,采用共沉淀法制备了x CeO2-y WO3/TiO2催化剂并研究了其抗硫性能。通入SO2后催化剂的脱硝温区向高温移动,其中25Ce6W和30Ce6W的催化剂仍能保持最高脱硝率在98%以上,且脱硝率90%和95%的温度区间最宽分别达到了315和285℃。30Ce6W催化剂经8 h抗硫实验,脱硝效率仅由95%降到92%,抗硫性能稳定。X射线衍射(XRD)、X射线光电子能谱(XPS)、比表面积测试(BET)、氨气程序升温脱附(NH3-TPD)、氢气程序升温还原(H2-TPR)等测试结果表明:25Ce6W和30Ce6W催化剂抗硫脱硝后催化剂表面吸附氧Oα的比例上升,利于NO的吸附及NO氧化为NO2从而对催化效果有一定的促进作用。而催化剂表面堆积硫酸铵与硫酸氢铵造成了催化剂孔隙堵塞及坍塌使比表面积和孔容减小,且催化剂表面Ce3+浓度降低,同时H2-TPR 580℃附近的还原峰向高温方向移动,从而降低了脱硝效果,但随温度升高硫酸铵与硫酸氢铵分解后,催化剂的活性提升。

China is facing the emission limitation of nitrogen oxide and the difficulty in handling dangerous waste of commercial catalyst(V2 O5-WO3/TiO2). In this paper,a novel method of preparing CeO2-WO3/TiO2 catalysts by impregnation-thermal decomposition was put forward. The effects of active component content of Ce and W on denitrification efficiency was studied. After inserting SO2,the denitration temperature zone of catalyst moved to the higher side. The catalysts of 25 Ce6 W and 30 Ce6 W could still maintain the highest denitration rate above 98%. Catalyst of 30 Ce4 W reached the widest temperature range 315 ℃ and 285 ℃ with a denitration efficiency 90% and 95%,respectively. After anti-sulfur experiment for eight hours,the denitration effiency of 30 Ce6 W catalyst merely declined from 95% to 92%,which showed its stable sulfur resistance. The structure and mechanism of catalysts were characterized by Xray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),specific surface area test(BET),ammonia programmed temperature desorption(NH3-TPD)and hydrogen programmed temperature reduction(H2-TPR),and the results showed that higher ratio of Ce4+and chemisorbed oxygen content on the surface of 25 Ce6 W and 30 Ce6 W after anti-sulfur and denitrification experiment and higher specific surface area were conducive to improving the denitrification performance. And the oxides on the surface were easier to be reduced and had a greater adsorption capacity for NO. Ammonium sulfate and ammonium hydrogen sulfate which accumulated on the surface caused the pore blockage and collapse of the catalyst.They reduced the specific surface area and pore volume. In addition,the concentration of Ce3+on the catalyst surface decreased,and the reduction peak near H2-TPR 580 °C moved toward the higher-temperature side. Therefore,the denitration rate declined. However,the activity of catalyst would improve once they decomposed with the improvement of temperature.