負載於Y型沸石之金鐵觸媒的製備及一氧化碳氧化之相關研究

Study on Preparation and Application of Y Type Zeolite Supported Gold-Iron Catalysts for CO Oxidation

洪健雄(Chien-Hsiung Hung)

指導教授 ： 萬本儒

國立臺灣大學/工學院/化學工程學研究所/碩士(2012年)

https://doi.org/10.6342/NTU.2012.00211

摘要

本研究的主要目的為製備高活性金鐵觸媒於Y型沸石上，應用於室溫一氧化碳之氧化反應，依據內容可分成兩大部分: (1) 探討製備程序對金鐵觸媒的影響，(2) 測試不同反應條件與儲存環境對於金觸媒活性的影響。觸媒性質的鑑定包含原子吸收光譜、X光繞射光譜、X光光電子能譜儀，以及比表面積量測儀。
研究結果顯示，鐵離子交換程序為金能否擔載於NaY沸石之關鍵，而硫酸亞鐵是該程序較適宜的前驅物。鐵沸石只要經過鍛燒程序，不論鍛燒的次序與溫度為何，之後所合成之金鐵觸媒的活性都會很低；而未鍛燒的鐵沸石，經過鹼處理程序後所製備的金鐵觸媒起始活性可達100 %，但會有衰退的問題。此外，未鍛燒之鐵沸石若不經鹼處理，製備出的金鐵觸媒會沒有活性。沸石的選擇上，以NaY沸石製備的金鐵觸媒(AuFeNaY)活性較高，其次為HY製備的金鐵觸媒(AuFeHY)，但是兩者都沒有比未擔載之金鐵觸媒(Au/Fe(OH)x)活性與穩定性來得高，代表欲製備高活性的金鐵觸媒則可能不適宜以沸石做為擔體。
本研究製備的金鐵沸石AuFeNaY與Au/Fe(OH)x於25 ℃的起始催化活性都能達100 %，但兩者活性都會劇烈衰退，且經過碳化矽的加入、金載負量的降低，與反應溫度的降低仍無法改善。最後發現，導入少量的水氣於反應氣體是解決活性衰退的最佳方法。推測之機制為:金鐵觸媒的催化反應會伴隨擔體表面氫氧基的消耗與碳酸鹽的累積，而水氣的加入不僅能補充氫氧基也能移除碳酸鹽，有助於維持觸媒的反應活性。
為了找出金鐵觸媒最適合的儲存環境，本研究測試金鐵觸媒在不同環境下儲存2個月之活性，結果並未觀察到由容器所引起的觸媒活性變化。儲存環境方面，Au/Fe(OH)x於真空、大氣與冷凍幾乎都可以維持100 %的活性；AuFeNaY則在常溫常壓儲存的活性會降至78 %，常溫真空儲存會降至85 %，而在冰箱儲存活性則為97 %，因此本研究建議儲存AuFeNaY在低溫冷凍的環境。

關鍵字

金鐵觸媒 ； 沸石Y ； 氧化鐵 ； CO 氧化反應

並列摘要

The purpose of this study is to prepare gold-iron catalysts on zeolite Y with high catalytic activity for CO oxidation at room temperature. The research can be divided into two parts: (1) Effects of preparation procedures on activity of gold-iron catalysts and (2) Effects of reaction conditions and storage environments on gold-iron catalysts. The catalysts were characterized by using AA, XRD, ESCA, and BET measurements.
From the experimental results, the following facts have been found: (1) Only trace amount of gold can be loaded on NaY. However, after ion-exchange process for substituting sodium with iron cations, gold loading can be be substantially increased. (2) Compared to Iron(Ш) nitrate, iron(II) sulfate is more suitable for ion-exchange because of lower acidity in the solution. (3) Poor catalytic activity of AuFeNaY was obtained, if iron-zeolite (FeNaY) was treated by 550 °C calcination before gold loading process. (4) High catalytic activity of AuFeNaY with an initial CO conversion 100 % (under tested conditions) was obtained, if uncalcined FeNaY was treated by using NaOH solution and dried prior to loading gold. However, its activity decay was severe. (5) Without NaOH solution treatment of iron-zeolite (FeNaY), the prepared AuFeNaY catalysts presented nearly no activity. (6) AuFeNaY catalyst prepared from NaY zeolite exhibited higher activity than that from HY. However, the above two catalysts showed lower activity than Au/Fe(OH)x catalyst, which was not supported in Y type zeolite.
The initial CO conversion of AuFeNaY and Au/Fe(OH)x at 25 ℃ achieved 100 %, but both activities decayed dramatically during reaction. Adding SiC inert in catalyst bed for increasing heat transfer area, reducing gold loading in the catalysts and decreasing reaction temperature, all can not improve the activity decay problem effectively. Finally, it has been found that the best way to reduce deactivation is to introduce a small amount of water vapor into the reactor. The presence of moisture may remove the carbonate produced in the reaction, according to the literature. Moreover, the water vapor may maintain the amount of hydroxide groups on iron species, which might be important to the activity of gold catalysts.
The effects of storage conditions (i.e., container, atmosphere and temperature) on catalytic activity of gold-iron catalysts have been investigated in this research. It has been found that, after two-mouth storage, the catalytic activity of AuFeNaY catalysts stored in refrigerator maintained 97 % CO conversion which is the highest in comparison to AuFeNaY stored in the other conditions. As to Au/Fe(OH)x, almost no change in catalytic activity was observed for catalysts stored in different conditions.
Au/Fe(OH)x possesses the best catalytic and the highest storage stability among the catalysts prepared in this research. To load iron and gold species on Y-type zeolites can not improve catalytic activity and storage stability. Therefore, there is no need to support gold and iron on zeolites for future application.

並列關鍵字

Gold-iron catalyst ； zeolite Y ； iron oxide ； CO oxidation

參考文獻

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