釕觸媒催化醋酸濕式氧化反應之研究

Wet Air Oxidation of Acetic Acid by Ruthenium Catalysts

黃耀賢(Yao-hsien Huang)

指導教授 ： 尋孝國

元智大學/工程學院/化學工程與材料科學學系/碩士(2001年)

摘要

溼式氧化法是工業上處理醋酸廢水的有效方法，而在各種的文獻報導中，貴重金屬一直是處理醋酸的有效物質之一，而二氧化鈰(CeO2)和活性金屬間之交互作用具有提升觸媒活性之作用，因此本研究的研究重點就是放在以貴重金屬Ru與CeO2負載於氧化鋁擔體上所形成的觸媒來處理醋酸。
本研究主要是針對醋酸(acetic acid)，以溼式氧化的原理，加入不同比例的Ru/CeOX/Al2O3觸媒，藉著反應的結果來分析觸媒活性的優劣，並藉由各種分析儀器的幫助進而分析出其造成反應活性加乘的原因來探討其微觀上的結構。探討為何在氧化鈰加成的比例增大時，反應會造成活性衰退的變因，由分析的結果發現除了Ru、CeO2的成份外，由於觸媒製備時還原溫度的不同，會影響著另一種成份Ce2O3的產生。
由實驗的結果也發現在去除Ce2O3的影響之後，觸媒氧化醋酸的能力大幅提升，並且其轉化能力會與CeO2含量呈現比的關係，CeO2和Ru間的電子轉移效應為造成Ru活性提升的重要因素，而當Ce2O3生成後其覆蓋作用反而造成觸媒活性降低。最後並利用實驗的數據結果來討論不同製備方法所製備完成的觸媒活性表現，導出其氧化醋酸的動力速率式。

關鍵字

濕式氧化 ； 釕

並列摘要

Wet oxidation (WO) can be an efficient and cost-effective technique for treatment of industrial wastewaters which are too toxic or concentrated for biotreatment and too dilute to incinerate. In a WO process pollutants in liquid phase are oxidized using air or pure oxygen at elevated temperatures. High pressures are also employed not only to keep the water in liquid phase but to increase dissolved oxygen concentration as well. The process can be operated at milder conditions if an appropriate catalyst is used. A heterogeneous catalyst is preferred to a homogeneous one since additional steps to remove the catalyst from the liquid after oxidation are not required. In WO processes many organic compounds gradually degrade to acetic acid, which is quite stable and invariably develop a resistance to further oxidation. Therefore, investigations on the catalytic kinetics of wet oxidation of acetic acid provide a convenient and direct means for catalyst development.
Among the various catalysts developed by other researchers for wet oxidation of acetic acid, Ru/CeO2 exhibits the best catalytic activity that is caused by the strong interaction between Ru and CeO2. Since supported ceria and bulk ceria may display different physical and chemical characteristics, in the present work we explored the catalytic characteristics of Ru/CeO2/Al2O3 catalysts for wet oxidation of acetic acid. Various contents of Ru and cerium oxide were deposited on Al2O3 powders by successive impregnation. Temperature-programmed reduction (TPR) was employed to study the reduction behavior of the catalyst precursors. TEM and SEM were used to observe the morphology of the prepared catalysts and XRD was employed for the identification of crystalline phases on the catalysts. Active surface area of Ru particles was examined by CO chemisorption. Reacting tests were carried out using a high-pressure stirred reactor in a semi-batch manner.
Experimental results revealed that the presence of Ru facilitated reduction reactions of CeO2 indicating that a strong interaction existed between Ru and CeO2. For the catalysts prepared by reducing at 450oC, Ce2O3 appeared and it migrated to the surface of Ru particles, thus resulting in a reduction of active surface area of Ru particles. Consequently, the catalyst activity decreased as the loading of CeOx increased. Reduction of active surface area of Ru particles was also found for the catalysts reduced at 300oC although it was not so serious as the catalysts reduced at 450oC. However, Ce2O3 was not detected by XRD and the catalyst with a higher CeO2 loading displayed better activity. No matter 300oC or 450oC was used for catalyst reduction, the catalysts containing cerium oxide exhibited higher activity than Ru/Al2O3 and this implicated that both the Ru-CeO2 and Ru-Ce2O3 interactions had an effect of promoting catalyst activity while the former was more pronounced than the latter.

並列關鍵字

Wet oxidation ； Ruthenium

參考文獻

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