過渡性金屬修飾銅鋅基質觸媒於室溫啟動催化部分甲醇氧化重組製氫反應之研究

The Study of Initiation of Partial Oxidation of Methanol Catalysis for Hydrogen Production at Room Temperature over CuZn-based Catalysts Modified by Transition Metals

王翠薇(Tsui-Wei Wang)

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(2008年)

摘要

Abstract

The co-precipitation method was used to prepare CuZn-based catalyst with platinum, manganese, and alumina. Their activity were tested in a fixed bed reactor with four reforming processes, i.e., decomposition of methanol (DM), steam reforming of methanol (SRM), partial oxidation of methanol (POM) and oxidative steam reforming of methanol (OSRM). The Cu/ZnO catalyst always initiated the POM and OSRM reaction at higher temperatures (~ 200 oC) and expressed relatively poor activity at the reaction temperature below 200 oC. The higher initiation temperature of POM required by Cu/ZnO was attributed to its high feasibility to form inactive CuOx structures in oxygen environments.
Cu30Ptx/ZnO (30 wt % Cu and x wt % Pt) catalysts were prepared by co-precipitation (CP) method. Fortunately, the Cu30Ptx/ZnO catalysts showed good performance in the OSRM at lower 200 oC. The Cu30Pt2/ZnO catalyst studied in the OSRM reaction had the highest conversion of methanol (C¬MeOH) and lower CO selectively (SCO) due to the reducibility of copper on the Cu30Ptx/ZnO catalysts would be enhanced attributed to existence of platinum. The in-situ XANES spectra of OSRM reaction over Cu30Ptx/ZnO shows that the conversion of methanol (CMeOH) would raise with the increment of unstable CuI species.
A series of Cu30Mnx/ZnO (30 wt% of Cu and X wt% of Mn) catalysts showed high catalytic activity due to the formation of CuMn2O¬4 phase. The CuMn2O4 phase plays an important role in catalytic reaction. Prepared Cu30Mnx/ZnO catalysts were tested with a process of POM. Noteworthy, Cu30Mnx/ZnO catalysts can initiate POM reaction at RT and produces a hydrogen rich gas at a low reaction temperature of TR = 150 oC. However, the Cu30MnxZn catalysts showed deactivation after 50 hrs due to aggregation of catalyst in the high temperature or using for a long time.
A series of Cu30Mn20Alx/ZnO (30 wt% of Cu, 20 wt% of Mn and x % of Al) catalysts showed high sustainability and durability in POM reaction attributed to the CuAl2O4 structure and avoids Cu sintering. The POM process exhibited a high methanol conversion (CMeOH >80%) but a poor hydrogen selectivity (SH2 < 90 %) and a high CO selectivity (SCO > 10%). However, time-on-stream experiments were performed at TR = 150 oC for a long time over Cu30Mn20Alx/ZnO catalyst and showed slight deactivation carrying out POM reaction for 80 hrs (CMeOH= 93 %). Thus, the Cu30Mn20Alx/ZnO catalyst was potential commerce and applied to PEMFC system in the future.

關鍵字

氫燃料電池 ； 重組器 ； 銅鋅觸媒 ； HASH(0x1c891780) ； HASH(0x1c891820)

並列摘要

本實驗內容是利用共沉澱法製鉑、錳或鋁修飾之Cu/ZnO基質觸媒，並以固定床反應器測試四種不同的甲醇重組程序的活性和選擇性，分別是甲醇分解(DM)、甲醇蒸氣重組(SRM)、甲醇部分氧化(POM)和甲醇氧化蒸氣重組(OSRM)反應。由於Cu/ZnO觸媒在200 oC以上有優異的活性，但是在低於200 oC活性卻不佳，其中可能的原因是，在高溫含氧的條件下，金屬銅容易被氧化成無活性的CuOx結構。
利用共沉澱法備製不同比重以鉑為修飾的Cu30Ptx/ZnO複合觸媒，進行OSRM反應。在低於200 oC以下，具有比Cu/ZnO觸媒更好的催化活性。尤其以Cu30Pt2/ZnO觸媒具有最高的甲醇轉化率(CMeOH)和低一氧化碳(SCO)選擇性。由於加入鉑可增加銅金屬的還原能力，X光吸收光譜近邊緣結構圖譜(XANES)指出即時監測的Cu30Pt2/ZnO催化劑進行OSRM反應時，在反應活性越好的時候具有CuI含量越多。
將不同比重以錳為修飾的Cu30Mnx/ZnO複合觸媒進行甲醇部分氧化反應發現，由於CuMn2O¬4 尖晶石的產生，使Cu30Mnx/ZnO具有良好的催化活性而此晶相在催化反應佔有極重要的角色。值得注意的是， Cu30Mnx/ZnO觸媒可以將甲醇部分氧化反應在室溫下起燃至150 oC。然而在進行50小時反應之後Cu30Mnx/ZnO觸媒之催化活性會因為銅金屬在高溫下團聚而逐漸失去活性。
Cu30Mn20Alx/ZnO 觸媒在鋁修飾之後發現有CuAl2O4的尖晶石結構產生，此晶相有助於觸媒在甲醇部分氧化反應上的穩定性以及耐久性。雖然Cu30Mn20Alx/ZnO觸媒在POM反應具有高甲醇轉化率(CMeOH >80%)，但是氫氣選擇率(SH2 < 90 %)和一氧化碳選擇率(SCO > 10%)卻不佳。然而將此觸媒在反應溫度(TR) 150 oC進行80小時長時間的POM反應測試之後，甲醇轉化率(CMeOH = 93 %)卻只輕微的降低而已，由此可知，Cu30Mn20Alx/ZnO 觸媒具有商業化以及應用在質子交換膜燃料電池上的潛力。

並列關鍵字

hydrogen ； fuel cell ； CuZn-based catalysts ； methanol ； reformer

參考文獻

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