活化條件對含浸法製備Au觸媒在CO+O2及NO+CO反應活性影響

The Activation of Supported Au Catalyst Prepared by Impregnation for CO+O2 and NO+CO Reactions

蔡欣諺(Hsin-Yen Tsai)

指導教授 ： 林昇佃

元智大學/工程學院/化學工程與材料科學學系/碩士(2005年)

摘要

本研究之研究目的是嘗試以含浸法製備出具有高催化CO+O2反應活性之金觸媒，並探討此高活性觸媒是否也具有高催化NO+CO反應活性。先前研究發現含浸法製備金觸媒的活性不好，本實驗利用NH4OH溶液含浸鹼處理及濕式鹼處理方法來活化觸媒，發現含浸鹼處理並無法改善含浸法觸媒活性不好的缺點，而經過濕式鹼處理方式則可以有效的提升Au/γ-Al2O3觸媒活性，在423K即可達到100％的CO轉化率，且經過O2鍛燒前處理後也能有效提升觸媒活性。
實驗測試發現濕式鹼處理方法中所用的鹼量是一個重要的參數，在足夠的鹼當量條件下，由EXAFS分析發現並沒有Au-Cl結構的存在，且利用AgNO3滴定濾液的結果也能確認此濕式鹼處理方式確實能夠將吸附在觸媒表面的Cl除去，減少Cl的影響，比較三種不同鹼液NH4OH、NaOH及NaBH4進行濕式鹼溶液處理，皆可以提升觸媒活性，不過經過NaBH4處理後觸媒的活性低於其餘兩種鹼處理過的觸媒，由XPS分析發現有B殘留在觸媒表面上，TEM分析則顯示有較寬的粒徑分佈，可能是此觸媒活性不好的原因。將含浸法製備之Au/TiO2觸媒經過此濕式鹼溶液處理也能夠有效地活化觸媒，再經過O2鍛燒前處理後也能更加提升觸媒活性，甚至與沈澱法觸媒或參考觸媒相比也不遜色，但對Au/TiO2-Al2O3觸媒則活化效果不佳，對於這些添加Ti的Au/TiO2-Al2O3觸媒中，僅添加Ti再配合高溫氫氣還原前處理也能有效提升觸媒的CO氧化活性，其中以含浸15％Ti的觸媒活性最好。
將這些具有高CO氧化活性之金觸媒進行NO+CO反應活性測試，發現經過具有較高CO氧化活性的NaOH處理之Au/γ-Al2O3觸媒及NH4OH處理之Au/TiO2觸媒，在NO+CO反應中也同樣具有較好的NO+CO反應催化活性。

關鍵字

金觸媒 ； 鹼處理 ； 含浸法

並列摘要

Previous studies show that the incipient-wetness impregnation method is never considered suitable for making supported Au catalysts. In this study, we tried to activate this supported Au catalysts by treating with NH4OH solution via an incipient-wetness impregnation or a wet treatment using excess solution. The alkali-treatment via an incipient-wetness impregnation can not activate the Au/γ-Al2O3 prepared by impregnation method. However, the wet-treatment using excess NH4OH solution effectively promoted the catalytic activity. A subsequant O2 calcination result in a very active catalyst for CO oxidation.
The Au/γ-Al2O3 prepared by impregnation can be activated by a wet-treatment with any of NH4OH(aq), NaOH(aq) and NaBH4(aq) for low-temperature CO oxidation. The NaBH4-treated catalyst is less active than that treated by either NH4OH or NaOH. The ratio of alkali to Au is important in such alkali treatment. NO Au-Cl bonding was found in the activated catalyst by EXAFS analysis, and the Cl removal was confirmed by AgNO3 titration. Such an alkali treatment is also effective in activating the Au/TiO2 prepared by an incipient-wetness impregnation for low-temperature CO oxidation. The activated catalysts have comparable activities as the Au/TiO2 prepared by a deposition-precipitation method or the Au/TiO2 reference catalyst. Attemps to add Ti onto Al2O3 by impregnation was found more active than Au/Al2O3 but less active than the Au/TiO2. The wet-treatment with excess alkali solution was less effective than a high-temperature reduction in activating the Au/TiO2-Al2O3.

並列關鍵字

Au catalyst ； Alkali treatment ； Impregnation