利用奈米級氧化鈰／氧化鈦類型觸媒催化亞甲基藍濕式氧化反應之研究

Study on Catalytic Wet Air Oxidation of Methylene Blue in Aqueous Solution via TiO2/CeO2 Type Nanocatalyst

本實驗以自製奈米級觸媒，包括CeO2、CeO2/HA（氫氧基磷灰石）、TiO2與CeO2/TiO2等四種，在高溫、高壓及供給氧氣環境下催化亞甲基藍之濕式氧化反應，並以染料的脫色率與COD去除率探討反應過程中觸媒對亞甲基藍之催化效能。研究結果顯示，在未添加觸媒情形下，氧分壓1.5MPa、100ppm亞甲基藍溶液，在CWAO反應下其脫色率及礦化率是隨溫度提升而增加，故亞甲基藍在特定溫度下，具有一定程度的熱分解行為。本研究使用之觸媒經由SEM、BET鑑定得知，CeO2、TiO2與CeO2/TiO2等三種觸媒粒徑約介於15~21nm，比表面積約介於39~47平方公尺/g，其中以TiO2觸媒有較小粒徑與較高比表面積，故其反應效能為四者最優，其在亞甲基藍100ppm、溫度180℃、觸媒添力量1g/L、氧分壓1.5MPa條件下，反應四小時後脫色率及礦化率分別為95%、38.5%。溫度從180℃到200℃時，TiO2觸媒催化亞甲基藍之COD去除率隨反應溫度上升而增加；但溫度從200℃到220℃時，COD去除率隨反應溫度上升而下降，故最適反應溫度為200℃。最適觸媒添加量為1.0g/L，少量觸媒添加(0.5~1.5g/L)可以形成較多自由基，添加過量觸媒(1.5~3.0g/L)則抑制自由基的產生。氧分壓以1MP之效能為最佳。TiO2觸媒之晶像強度隨煅燒溫度之增加而加強，但以515℃煅燒之觸媒因結構缺陷較多，故其處理亞甲基藍之效能優於300℃與700℃煅燒者。

In this study, four nano catalysts including CeO2、 CeO2/Apatite、 TiO2 and CeO2/TiO2 were prepared for the catalytic wet air oxidation of methylene blue. Via rate of color removal and COD removal, performance of the catalysts was evaluated to screen for the optimal one and reaction condition of the most active catalyst was also investigated. The results indicated that the efficacy of WAO without catalyst of 100ppm methylene blue improved with temperature at O2 partial pressure of 1.5Mpa, which implied heat decomposition occurred in a certain temperature. The characterization of catalysts of SEM showed the diameter of CeO2、TiO2 and CeO2/TiO2 catalysts are around 15 to 21nm, and the BET analysis were around 39 to 47m^2/g. With the smallest diameter and largest surface area, TiO2 catalyst performed the most active among the four. At the condition of 100ppm methylene blue concentration, 180℃, 1.0g/L the catalyst loading and 1.5 MPa of O2 pressure, the color removal and COD removal after 4 hrs reaction were 95% and 38.5%, respectively. The rate of COD removal at temperatures of 180~200℃ increased as reaction temperature increased, while at temperatures of 200~220℃, the COD removal decreased with increase m reaction temperature, suggesting an optimum temperature for the operation of this catalyst of 200℃. An optimal loading was found at 1.0g/L, when free radical formation was higher at a lower catalyst loading (0.5~1.5g/L), while at a higher loading (1.5~3.0g/L), free radical destruction dominated. The suitable O2 partial pressure occurred at 1.0Mpa. The intensity of the TiO2 crystals peaks increased as calcinations temperature increased, while the 515℃ calcinated-temperature catalyst was superior to 300℃ and 700℃ calcinated-temperature catalyst on CWAO performance with his more structure defects.