金為貴重金屬，是一種非常穩定且不與其它物質發生反應；但在奈米尺寸下，奈米級的金擔載於金屬氧化物時，可在低溫下將一氧化碳氧化而生成二氧化碳。CO是一種有毒、無色無味的氣體，通常在燃燒不完全時會被產生。觸媒對於空氣清淨及降低空氣污染的重要性日益漸增，CO氧化反應對環境保護是非常重要的。日本的Haruta教授提出，當金利用含浸法、共沉澱法及沉積沉澱法，將奈米金擔載於金屬氧化物上，其金觸媒可在200 K下將CO氧化。對於金觸媒的活性影響包括擔體選擇、製備方法及製備條件。 本研究利用添加不同的促進劑改變擔體的電子效應及幾何效應。本研究利用添加銅及鈷作為促進劑於二氧化鈦中進行擔體的改質，利用初溼含浸法將金屬硝酸物水溶液加入Evonik-Degussa 公司所提供的TiO2 (P-25)，均勻混合後煅燒再使用沉積沉澱法將金沉積於擔體上。所製備出來的金觸媒分別以感應耦合電漿質譜分析儀(ICP-MS)、X光繞射分析儀(XRD)、穿透式電子顯微鏡(TEM)、高解析穿透式電子顯微鏡 (HRTEM)及X光電子能譜儀(XPS)等儀器來鑑定其物理及化學性質。反應以固定床，反應器填充0.05 克觸媒，並以進料為1% CO 在空氣中，總流量為100 ml/min 及150 ml/min 進行反應。 使用沉積沉澱法可得到高分散性及較小的粒徑分佈，但無法將金完全的擔載於擔體上。本研究所使用的兩種不同的促進劑添加於Au/TiO2中，其促進劑皆可增加觸媒活性。銅及鈷增加觸媒活性的原因不同。銅作為促進劑的觸媒中，以Au/5% CuOx-TiO2為最佳觸媒；鈷作為促進劑的觸媒中，以Au/3% CoOx-TiO2為最佳觸媒。使用兩者最佳觸媒進行長時間耐久測試中，以Au/3% CoOx-TiO2較佳。本研究中成功製備出最適含量的促進劑添加於Au/TiO2進行擔體的改質，並且在WHSV=180,000 ml/h g下，可將CO完全氧化。 Massive gold was a stable and precious metal; it is not an active catalyst. In nanosize scale,the nano-gold supported on the metal oxide could oxidize CO at low temperature and produced carbon dioxide. CO was a toxic, colorless and tasteless gas; it is produced by the fuel without complete oxidation. The most extensively studied reaction in the history of heterogeneous catalysis is becoming increasingly important in the context of cleaning air and lower automotive emissions. The reaction is important for environment protection. When gold is deposited as nanoparticles on metal oxides by impregnation, co-precipitation and deposition-precipitation (DP) techniques, it exhibits surprisingly high catalytic activity for CO oxidation at a temperature as low as 200 K. The activity of gold catalysts also depends on support, preparation method and condition. The promoters were added in Au/TiO2 to change the support properties, including electronic effect and geometric effect. In this study, the effects of promoter such as Cu and Co were investigated. The support was prepared by incipient-wetness impregnation with aqueous solution of nitrate salt. TiO2 was supplied by Evonik-Degussa Company (P-25). A series of Au catalysts was prepared by deposition-precipitation (DP) method and the pH value was 7. The catalysts were characterized by inductively-coupled plasma-mass spectrometry (ICP-MS), temperature programming reduction (TPR), X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). The reaction was carried out in a fixed bed reactor with a feed containing 1% CO in air at WHSV=120,000 ml/h g and WHSV=180,000 ml/h g. High gold dispersion and narrow size distribution was obtained by DP method. Two different promoters were added in Au/TiO2, which were also enhanced the activity on CO oxidation. Cu and Co have different promotive effect. Au/5% CuOx-TiO2 was the best catalyst in a series of Au/CuOx-TiO2 and the Au/3% CoOx-TiO2 was the best catalysts in a series of Au/CoOx-TiO2. Au/3% CoOx-TiO2 had better stability than Au/5% CuOx-TiO2 catalyst. In this study, we have successfully prepared the catalysts at suitable content with very high activity on CO oxidation.
