二氧化鈰奈米管的製備與其催化反應之研究

Abstract

本研究係以不同條件製備型態均勻且具高表面積的二氧化鈰奈米管，探討因素包括水熱時間、水洗條件、水熱溫度、鹼液濃度及煅燒溫度。利用粉末X光繞射(XRD) 、掃描式電子顯微鏡(SEM)、穿透式電子顯微鏡(TEM)、氮氣等溫吸脫附為分析工具，探討觸媒組成與其結晶性、型態分佈及表面積。實驗顯示在鹼液濃度為0.6 M，於120 °C水熱24小時，水洗到pH = 9時可得到尺寸分佈一致，直徑約為146 nm，且其表面積最大(S.A. = 73 m2/g)的二氧化鈰奈米管。以450 °C在氧化環境下煅燒可得到具有結構缺陷可促進晶格氧的移動，且完整的二氧化鈰奈米管擔體，以此擔體所製備的鉑觸媒在一氧化碳氧化反應有不錯的活性。 為了解鉑觸媒之顆粒大小、氯含量與金屬氧化態對一氧化碳氧化反應能力之影響，改變製備方法、前處理與活化條件，實驗顯示以初濕含浸法製備的二氧化鈰奈米管擔體鉑觸媒之鉑顆粒最小(d = 3 nm)，接續以還原水洗前處理之鉑觸媒的殘餘氯含量最少。為得到最佳一氧化碳氧化反應之表現，在還原氣流下以200 °C活化觸媒，可使二氧化鈰奈米管擔體鉑觸媒發揮最佳的活性表現(T50 = 76 °C)。 以原位光譜分析技術探討二氧化鈰奈米管擔體鉑觸媒之乙醇直接分解（Decomposition of Ethanol, ED)、部分氧化（Partial Oxidation of Ethanol, POE）與蒸氣重組（Steam Reforming of Ethanol, SRE）反應活性與機制。結果顯示在SRE反應中，二氧化鈰奈米管擔體鉑觸媒在室溫即可促進乙醇分解並且產生大量的氫氣，與商用二氧化鈰擔體鉑觸媒比較，其活性與氫氣產生量均有良好的表現。Shape-controlled synthesis of CeO2 has drawn lots of attention in the decade. Especially tubular nanostructures have received significant interest since the unique physical and chemical properties. In the present work, CeO2 nanotubes (CeNT) have been fabricated via a hydrothermal method through controlling reaction time, acid washing conditions, reaction temperature, concentration of alkaline solution, and temperature of calcination. The properties of the CeO2 nanotubes were characterized by N2-isotherm sorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Three kinds of methods are chosen to prepare ceria-nanotubes supported platinum (Pt/CeNT) catalysts: incipient wetness impregnation, impregnation, and sodium borohydride reduction method. Application of catalysis over Pt/CeNT catalysts focus on the CO oxidation (evaluation in the micro flow-reaction) and ethanol reforming (studies with the in-situ spectra) reactions. In the CO oxidation reaction, the residual chlorine on the Pt/CeNT catalyst plays an important role in determining the catalytic activity. Combination of in-situ FTIR and TPD-MS techniques to investigate the catalytic performance and mechanisms of ethanol reforming reactions (including decomposition, steam reforming, and partial oxidation of ethanol). The results show the activities of ethanol reforming over Pt/CeNT catalyst is better than the Pt/CeO2(C) catalyst.