應用在甲醇重組反應中之金修飾銅鋅觸媒的合成、特性及反應性探討

The study of synthesis method, reactivity and ignition temperature over gold promoted copper zinc catalyst

黃科倫(NG KE LUN)

指導教授 ： 黃鈺軫

國立清華大學/原子科學院/生醫工程與環境科學系/碩士(2010年)

摘要

本篇研究將探討奈米金顆粒沉積在銅鋅催化劑上進行甲醇重組反應。由研究顯示先利用共沉澱法合成銅鋅觸媒，經乾燥後再以沉積沉澱法在pH 7條件下將金沉積到銅鋅上，可有效減少金在合成過程中的流失，經鍛燒後可得到的較佳催化活性之金銅鋅觸媒。本篇研究以金重量百分比分別為0%，0.8%，3%，與4.3%，而銅含量保持為30%之催化劑進行特性鑑定並在固定反應床進行甲醇部分氧化反應，甲醇蒸氣重組反應與氧化性甲醇蒸氣重組反應之活性測試。
研究顯示金的添加能夠有效的降低反應中的一氧化碳濃度，且隨著金的添加量增加而減少。此外，在無氧的環境下（甲醇蒸氣重組反應），金的添加銅同樣能夠減少一氧化碳的形成。而利用較高濃度的氧氣進行反應並不能有效的降低甲醇部分氧化反應中一氧化碳的生成，反而造成嚴重的氫氣燃燒反應，並且在甲醇氧化蒸氣重組反應中，高濃度的氧反而導致更多的一氧化碳生成。
此外，我們也發現添加金能夠在較低的溫度啟動重組反應。藉由X光吸收光譜儀可以發現在150oC時只通甲醇且未預還原的情況下，Au4.3Cu30ZnO已經被還原成63%Cu0以及37%Cu+，而Cu30ZnO則維持在氧化銅的狀態，金的添加讓觸媒上的銅更容易的被甲醇還原。同時，在室溫下將甲醇通入還原後的Au4.3Cu30ZnO以及Cu30ZnO，發現Au4.3Cu30ZnO有較多的氧化亞銅以及氧化銅的形成，代表金的添加增加了更多的金銅介面，能夠吸附更多的甲醇。而在不同氧醇比的甲醇部分氧化反應中，Au3Cu30ZnO觸媒由0.1氧醇比的180oC 啟動溫度下降至0.7氧醇比的120oC，而Cu30ZnO只有10oC的差別，金對氧較佳的吸附能力改善了啟動溫度。
總結而言，金是一個用以降低反應啟動反應溫度與降低一氧化碳生成的理想添加劑。金的添加在未經過還原處理的情況下降低了啟動溫度，使得重組器能夠在更少的加熱模組與操作溫度下產生氫氣。

關鍵字

金 ； 啟動溫度 ； 一氧化碳

並列摘要

Nano gold particle supported on copper zinc catalyst to proceed methanol reforming was investigated in this study. A synthesis method was developed which utilized co-precipitation to produce copper zinc catalyst, gold was added at pH 7 by deposition precipitation method after copper zinc catalyst was precipitated and dried. This synthesis procedure avoids severe gold loss and preserves significant reactivity after calcination. Different gold content, 0%, 0.8%, 3% and 4.3%, on the 30%copper supported on zinc oxide catalyst synthesis by procedure mentioned above, were characterized and tested in a fixed bed reactor through partial oxidation of methanol (POM), steam reforming of methanol (SRM) and oxidative steam reforming of methanol (OSRM) reaction.
The addition of gold can suppress the carbon monoxide. In addition, with the increasing gold content, less CO is formed. Furthermore, in the absent of oxygen, addition of gold also decrease the CO formation in SRM reaction. Higher oxygen concentration in POM reaction did not decrease the CO formation significantly, but causing severe hydrogen combustion. Meanwhile, higher oxygen concentration in OSRM reaction leads to higher CO formation.
Besides, the addition of gold can lower the initiation temperature. In-situ XAS revealed that without pre-activation, there was no any CuO reduced by methanol on the Cu30ZnO. In contrast, 63% Cu0 and 37% Cu2O were observed on Cu30ZnO with 4.3% gold promoter. Meanwhile, methanol was passed through reduced Au4.3Cu30ZnO and Cu30ZnO at room temperature, Au4.3Cu30ZnO was found having more Cu2O and CuO species which represent more methanol was absorbed on the interface between copper and gold. Besides, we also discovered the initiation temperature of Au3Cu30ZnO was lower to 120oC when 0.7 O/M ration was used in POM reaction while Cu30ZnO was remain at 190oC. Better oxygen absorption ability of gold improved the initiation temperature.
Gold is an ideal additive to improve the initiation temperature and decrease CO formation. Lower initiation temperature without pre-activation allow simpler heating module and reduce cost for the reformer.

並列關鍵字

gold ； initiation temperature ； CO

參考文獻

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