| 摘要: | 本研究利用含浸法合成不同擔體之CeO2擔體觸媒，並測試不同反應條件對於含酚廢水WAO反應之影響，並以此實驗篩選出最佳擔體觸媒與最適操作條件。研究結果顯示，在所測試擔體(γ-Al2O3、SiO2、TiO2與Active carbon）結果顯示，以Ce/γ-Al2O3活性最好，Ce含浸量16.7wt.%、反應溫度180℃、酚濃度1000ppm、觸媒添加量3g/L、氧分壓1.5MPa時，反應4小時之酚轉化率將近40%COD去除率可達30%，而無添加觸媒之WAO反應4小時酚轉化率僅約為6%COD去除率約2%證實添加Ce/γ-Al2O3觸媒確實有其催化效能；經過整體反應效能評估最適操作條件為：Ce含浸量15wt.%、反應溫度200℃、酚濃度1000ppm、觸媒添加量1g/L、氧分壓1.5MPa，反應2小時可達酚轉化率95%COD去除率70%；本研究亦對使用過後之觸媒進行回收再生之探討，發現最適再生方法為無水酒精淋洗，再生後於反應溫度200℃、酚濃度1000ppm、觸媒添加量1g/L、氧分壓1.5MPa下，反應3小時可達99%酚轉化率及85%COD去除率，耐用性尚屬不錯。此外本試驗亦有誘導期之現象產生，由實驗發現反應溫度由180℃提升至200℃可使誘導期由4小時縮減至1小時。
在觸媒鑑定方面，吾人嘗試利用XRD、BET、O2-TPD、H2-TPR驗證觸媒活性高低之原因。由XRD圖譜之中，可以發現到隨著Ce含浸量增加，CeO2晶相成分亦增加，所以波峰隨之增強，但亦造成表面金屬團聚現象，使得活性位址並無增加，而有一最適Ce含浸量15wt.%，經由BET分析4.8wt.%、9wt.%、13wt.%、15wt.%、16.7wt.%、20wt.% Ce/γ-Al2O3觸媒表面積，分別為194.22、180.75、168.11、154.61、147.30、140.14(m2/g)，顯示不同Ce含浸量有著不同之比表面積，而由實驗結果得知最佳活性觸媒為15wt.% Ce/γ-Al2O3次佳為20wt.% Ce/γ-Al2O3，顯示出反應效能之優劣與比表面積並無直接之關係，活性高低主要受到觸媒之活性位址多寡而影響。在O2-TPD圖譜中雖未能顯示出15wt.%觸媒有較多之可交換之結構氧，但可證實擔體觸媒確實有其催化效能，而由H2-TPR圖譜中發現15wt.%觸媒的氫消耗量最高，表示其被還原之鈰含量最多，相對的鈰在擔體表面上的分散度較佳，亦佐證其為最佳活性擔體觸媒。
In this study, we prepared several supported ceria catalysts (supporter: γ-Al2O3, SiO2, TiO2 and Active carbon) via impregnation method for the CWAO of phenol to assess performance of supported ceria catalyst. By the rate of phenol conversion and the efficacy of COD removal, Ce/γ-Al2O3 was found to be the most active catalyst among the four tested. Using Ce/γ-Al2O3 (Ce content 16.7wt.%) and 180°C, 1.5MPa O2 and 3.0g/L catalyst loading, 1000ppm phenolic solution, could attain about 40% phenol conversion and 30% COD removal, after 4 hrs reaction. Under the same conditions, effectiveness of reaction without catalyst was only about 6% phenol conversion and 2% COD removal, showing that the Ce/γ-Al2O3 catalyst is a feasible alternative to CeO2 for the CWAO of phenol because it remains an effective catalyst and is cheaper to be prepared. The optimal reaction condition of CWAO of phenolic wastewater using Ce/γ-Al2O3 catalyst with 15wt.% Ce content is as follows: 200°C, 1.5MPa O2 and 1.0g/L catalyst loading. With the optimal condition, 1000ppm phenolic solution, after 2 hrs reaction, could attain about 95% phenol conversion and 70% COD removal. Moreover, various regeneration methods were also tested to identify the most efficient one. The most efficient regeneration method is rinsing the used catalyst with anhydrous alcohol. Under the same condition after 3 hrs, 1000ppm phenolic solution as the optimal one, could attain about 99% phenol conversion and 85% COD removal. This also demonstrates the good durability of the catalyst. Note that the induction period was found in the reaction, which was 4 hrs at 180°C and 1 hrs at 200°C.
The effectiveness of various supported ceria catalysts for CWAO of phenol was further demonstrated via BET, XRD, O2-TPD and H2-TPR. XRD analysis reveals that more Ce content corresponds to more CeO2 crystals, but the agglomeration is also higher as to the active sites are reduced. By BET analysis, it was found that the surface area of Ce/γ-Al2O3 has no apparent effect on its catalytic activity. The superior activity of Ce/γ-Al2O3 with 15wt.% Ce content was confirmed by H2-TPR, which showed that 15wt.% Ce/γ-Al2O3 had the highest H2 consumption. |
