金屬鈷(Co)附載於不同氧活性之載體(CeO2, BZDy)對乙醇氧化蒸氣重組反應之影響與反應路徑探討

The Mechanistic Study of Oxidative Steam Reforming of Ethanol (OSRE) over Cobalt on CeO2 and Dy-doped BaZrO3

邱耀慶(Ciou Yao-Cing)

指導教授 ： 王禎翰

國立臺灣師範大學/理學院/化學系/碩士(2017年)

https://doi.org/10.6345/NTNU202202016

摘要

本實驗使用10 %金屬鈷(Co)分別附載於親氧性之氧化鈰(CeO2¬)與親水性之鋯酸鋇參雜鏑(BZDy)上進行乙醇氧化蒸氣重組反應之探討。催化劑的製備方法為含淨法，催化劑之鑑定使用粉末繞射分析儀(XRD)、能量散射光譜儀(EDS)、程序升溫還原反應(TPR)與X光光電子光譜(XPS)進行。反應之測定使用氣相層析儀(GC)分析產率與選擇率之結果、in situ漫反射傅立葉轉換紅外光譜儀分析反應中間物與程序升溫還原反應(TPR)分析催化劑之狀態。在水與乙醇比例為1:7下，改變氧氣比例之反應，產率與選擇率結果之部分，當C/O ratio約為0.61，在Co/CeO2氫氣最高產率為77 %，CO/CO2選擇率分別為37 % / 59 %，CH4選擇率低於1% ，而Co/BZDy在C/O ratio = 0.61，最高氫氣產率為80 %，CH4/CO2選擇率分別為12 % / 83 %，而CO選擇率低於1 % ；水與乙醇比例為1:1、1:3與1:7時，Co/CeO2之最高氫氣產率分別在C/O ratio = 0.7為51 %、在C/O ratio = 0.6為76 %與在C/O ratio = 0.6為77 %，而Co/BZDy分別在C/O ratio = 0.7為60 %、在C/O ratio = 0.6為74 %與在C/O ratio = 0.6為81 %，由氫氣產率變化的結果表示Co/BZDy較Co/CeO2雨水反應之能力強；在水與乙醇比例為1:7下，C/O ratio為0.61時，改變溫度之結果氫氣產率可以顯示不同載體對氧與水受溫度影響之狀況，在溫度為450oC到600oC，Co/CeO2最高為45 %，而在350oC到450oC時，Co/BZDy之最高氫氣產率為150 % ，此顯示Co/CeO2較易與氧氣反應，造成H2被氧化為H2O，而Co/BZDy較易與水反應，使H2O之H形成H2。在in situ DRIFT之光譜結果顯示出 Co/CeO2與Co/BZDy之反應中間物皆出現acetate (CH3COO)，而其在不同載體之催化劑上會因親氧性與親水性的不同產生不同的細微變化：Co/CeO2因CeO2造成親氧性較強，使acetate斷C—C鍵後生成之COO易於離去生成CO/CO2，而CH3分解為C與H產生CO、H2、H2O；Co/BZDy因BZDy親水性較強，使acetate斷C—C鍵後生成之COO形成CO2，而CH3與水產生之H形成CH4。由反應後之TPR結果顯示，Co/CeO2¬¬之Co反應時為Co0之狀態，而Co/BZDy反應時之Co形成Co3+之狀態。由此三者分析之結果，推論出Co/CeO2¬與Co/BZDy之可能反應路徑。

關鍵字

乙醇氧化蒸氣重組反應 ； 鈷 ； 氧化鈰 ； 鋯酸鋇參雜鏑 ； 鈣鈦礦 ； DRIFT

並列摘要

The oxidative steam reforming of ethanol (OSRE) over cobalt on oxygen-active CeO2 and steam-active dysprosium doped BaZrO3 (BZDy) was investigated with various ethanol/oxygen/steam compositions at 400oC. The catalysts were synthesized with impregnation method and characterized by X-ray diffraction (XRD), Energy-dispersive X-ray spectroscopy (EDS), temperature programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS). The results found that 10% Co was successfully composited on both CeO2 and BZDy with two oxidation states, Co0 and Co3+. The catalytic products were analyzed with gas-chromatography (GC), and the intermediates were identified by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTs). The reforming results found that the catalytic reaction can be activated at 400oC with the 100% ethanol conversions efficiency and 80% hydrogen yield at high oxygen and steam ratios (specify ratio and catalysts). The selectivity of acetaldehyde decreased by the increased oxygen and steam ratios. The product of ethylene (C2H4) was negligible. The selectivity of CO2 was high on both catalysts and is higher over Co/BZDy (66 %) than Co/CeO2 (36 %). However, the selectivities of CO and CH4 are much different. The selectivity of CO was varied from 50% to 90% and that of CH4 was less than 1% over Co/CeO2.On the other hand, the selectivity of CO was less than 1% and that of CH4 was varied from 30% to 50% over Co/BZDy. The difference between Co/CeO2 and Co/BZDy corresponded to the key intermediate of acetate (COO), identified by DRIFT at 1450 cm-1 and 1550 cm-1. For Co/CeO2, the acetate (COO) became less with increased temperatures or oxygen contents, responsible for the high CO/CO2 selectivity; on the contrast, it was abundant on Co/BZDy, responsible for high CH4/CO2 selectivity. The different catalytic mechanisms on the two catalysts indicate that the oxygen active supporter (CeO2) provided oxygen for facilitating the formation of CO/CO2 and the steam active supporter (BZDy) supplied not only oxygen but also hydrogen to compose CH4/CO2. The TPR results after OSRE found that Co0 is abundant on Co/CeO2 while plenty Co3+ is found Co/BZDy.

並列關鍵字

oxidative steam reforming of ethanol ； cobalt ； CeO2 ； BZDy ； perovskite ； DRIFT

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