前此研究中已證實，高熱衝擊之CeO2觸媒對於含酚廢水之濕式氧化反應(Wet Air Oxidation, WAO)具有很好之催化效能。但是CeO2觸媒並不便宜，而且純CeO2之單位質量活性位址較少，為減少觸媒使用量以降低成本，並藉由增加觸媒分散度以維持與CeO2相當之活性，本研究首先利用初濕含浸法合成不同擔體之CeO2擔體觸媒，並測試其對於含酚廢水WAO反應之催化效能，以篩選出最佳活性者。接下來，利用O2程溫脫附(O2-TPD)與H2程溫還原(H2-TPR)等方法，探討造成活性差異之原因。研究結果顯示，在所測試擔體中(-Al2O3、SiO2、TiO2、AlPO4-5、commercial CeO2)，以CeO2/-Al2O3活性最佳，當反應溫度為180℃，添加3.0g/L含浸量20wt.%之CeO2/-Al2O3觸媒時，對於1000ppm含酚廢水2小時反應之轉化率可高達近100%，COD去除率亦達到約80%。再者，CeO2/-Al2O3活性較高，由O2-TPD結果顯示是因為具有較多之可交換結構氧，而H2-TPR結果則顯示其有較強之氧化反應活性位址，及較分散之CeO2。另外，觸媒耐用性亦經由使用過觸媒之活性測試加以評估，結果顯示因為積碳關係，造成觸媒活性大幅降低(2小時酚轉化率降至37%)，此可由EDS結果加以證明；在空氣中重新煅燒觸媒以提高積碳去除率，可有效提高觸媒之再生成效(2小時酚轉化率86%)。比較CeO2/-Al2O3與純CeO2之催化成效，雖然前者較差，但在價格優勢下，CeO2/-Al2O3對於含酚廢水CWAO仍具可行性。 It has been shown that the CeO2/-Al2O3 catalyst is a feasible alternative to CeO2 for the catalytic wet air oxidation (CWAO) of phenol because it remains an effective catalyst and yet is cheaper to prepare. In this study, we found that the optimal cerium content in the CeO2/-Al2O3 catalyst was 20 wt.%, regardless of catalyst loading. Furthermore, at 180℃, with a phenol concentration of 1000 mg L－1, and an O2 partial pressure of 1.0 MPa or 1.5 MPa, the optimal catalyst loading was 3.0 g L－1. The efficacy of CWAO of phenol improved with O2 partial pressure, although the effects of O2 pressure were more significant between 0.5 MPa and 1.5 MPa than between 1.5 MPa and 2.0 MPa. After 2 h of reaction, approximately 100% phenol conversion and 80% total organic carbon (TOC) removal was recorded at 180℃, 1000 mg L－1 of phenol and 3.0 g L－1 of catalyst. Because these percentages subsequently leveled off, it is suggested that 2 h is a suitable time over which to run the reaction. The efficacy of CWAO of phenol decreased as initial phenol concentration was raised (from 400 to 2500 mg L－1), with the exception of phenol conversion after about 2 h, for which 400 mg L－1 produced the lowest phenol conversion figure. Higher phenol concentrations require both catalyst loading and O2 partial pressure to be increased to maintain high performance. For example, for 2000 mg L－1 and 2500 mg L－1 phenol, nearly 100% phenol conversion and 90% TOC removal after 4 h of reaction at 180℃ required 4.0 g L－1 of catalyst and 2.0 MPa.
