使用含銅廢水修飾稻殼氧化矽控制模擬燃煤煙氣中Hg0與NO研究

Abstract

空氣污染的問題在近幾年受到相當多關注，燃煤電廠又是重要的固定污染源，因此其所排放的空氣污染物也受到一定程度的重視。其中汞(Hg)的高毒性和生物累積性，以及由NOx所衍生的酸雨、光化學煙霧與PM2.5，也使燃煤電廠所排放的Hg和NOx吸引了更多關注。本研究利用面板業製程之銅離子廢水改質稻殼氧化矽觸媒，嘗試降低合成材料的成本並同時將廢棄物資源化。改質比例為10, 25, 50 wt%的Cu搭配10wt%的Ce，材料則進一步用於模擬燃煤煙氣中Hg與NOx的去除。 研究結果顯示，經過銅離子廢水、CeOx改質後，材料的比表面積(SBET)有明顯的提升；而在所有樣品中，50%Cu-10%Ce/SiO2具有最大的比表面積(SBET= 260 m2 g-1)。XRD結果顯示在所有CuOx/SiO2樣品中，CuOx具有高度分散性或以無定形結構存在。由SEM和TEM圖可以觀察到，在經過金屬氧化物改質後原本均勻的球狀顆粒轉變為板狀顆粒結構，證實了改質後結構的改變。XPS的分析顯示Cu2+以及Ce4+為材料表面主要的金屬價態。H2-TPR與NH3-TPD的結果顯示50%Cu/SiO2與50%Cu-10%Ce/SiO2材料具有較其他材料更好的氧化還原能力以及更多的表面酸位。 測試結果顯示CuOx與CeOx的改質有效的提升了材料去除NOx、Hg的效果。其中50%Cu-10%Ce/SiO2材料具有最好的NOx去除效率，其在寬廣的溫度操作窗口下(150−300°C)展現了70−85%的deNOx效率。50%Cu/SiO2則具有最佳的除汞效率，在150°C時去除效率為88.2%；在250°C時Hg的去除效率幾乎維持不變。以上結果顯示使用含銅廢水改質稻殼氧化矽對於Hg與NOx的去除有高度的潛力。

Air pollution is receiving more and more public concern in recent years. Since coal-fired power plants (CFPPs) is one of the major stationary sources, the air pollutants emitted from CFPPs have attracted many attentions. Mercury (Hg) and NOx emitted from CFPPs have both received special concern owing to the high toxicity and long retention time in the environment of Hg and the formation of acid rain, photocatalytic smog, and secondary PM2.5 from NOx. In this study, a series of CuOx-CeOx/SiO2 catalysts were prepared via rice-husk-derived silica modified with copper-ion containing wastewater from panel industry for control of Hg0 and NO emission from simulated coal-combustion flue gases. Cu of 10, 25, and 50 wt% and Ce of 10 wt% was incorporated with the rice-husk-derived SiO2. The N2 adsorption result showed that the presence of Cu and Ce oxides increased the specific surface area (SBET) of SiO2 as compared to the raw sample. 50%Cu-10%Ce/SiO2 having the largest SBET may lead to its high NO removal efficiency. Surface-treated catalysts were examined with XRD; results showed that significant peaks of CuO were not detected among all the CuOx/SiO2 samples, indicating that CuOx was highly dispersed on the surface. SEM and TEM images showed that the uniform spherical particles have changed into plate-like structure, which can further confirm the occurrence of structural rearrangement after incorporated with metal oxides. XPS results showed that Cu2+ and Ce4+ were the major valence states presenting in the SiO2 catalysts. H2-TPR and NH3-TPD indicated that the 50%Cu/SiO2 and 50%Cu-10%Ce/SiO2 catalysts had greater redox ability and stronger acidity as compared to those containing smaller amounts of CuOx and CeOx. The modification of Cu and Ce was shown to successfully improve the NO removal efficiency. 50%Cu-10%Ce/SiO2 showed the best NO conversion efficiency of 70−85% with a broad temperature window of 150−300°C. 50%Cu/SiO2 catalyst exhibited greatest total Hg removal efficiency of 88.2% among all the tested catalysts under flue gas condition at 150°C and remained almost the same removal efficiency at 250°C. These results indicate that using rice-husk-derived SiO2 incorporated with copper recycled from industrial wastewater can be a feasible way for control of Hg0 and NO emissions.