| 摘要: | 奈米金觸媒於對-氯硝基苯氫化反應上有很好的催化活性和選擇性，此研究中，主要為氧化鈷及金屬鈀對金觸媒在對-氯硝基苯氫化反應活性的影響。氧化鈷方面，先以硝酸鈷含浸於二氧化鈦，之後以沉積沉澱法將金擔載於擔體上，製備一系列部不同鈷/鈦莫耳比的Au/CoOx-TiO2觸媒。而金屬鈀則比較不同還原方法對反應活性的影響，探討最佳的反應觸媒。以感應耦合電漿質譜儀、X光繞射儀、穿透式電子顯微鏡、高解析度穿透式電子顯微鏡、X光能譜散佈分析儀、程式升溫還原分析法和X光光電子能譜儀等儀器鑑定其物理、化學特性和表面性質；利用液相選擇性對-氯硝基苯氫化反應來測試觸媒的活性與選擇性，反應條件設定在：反應器為半批式反應器 (Parr Reactor Model 4842)；反應溫度為353 K；壓力為1.2 MPa；攪拌速率500 rpm；反應溶劑為甲醇；結果顯示適量的鈷加入，能強化觸媒的熱穩定度、活性位置的分散性，提升反應的活性和選擇率，在反應時間為180分鐘，p-CNB轉化率達80%時，對主產物對-氯苯胺的選擇率皆大於90 %，其中以鈷/鈦之莫耳比為1/9之觸媒活性表現最佳。而後針對(0.1 wt. %)金(0.01 wt. %)鈀觸媒分別以氫氣還原及硼氫化鈉還原進行探討，在相同的反應條件下，結果顯示鈀能有效提升反應物的轉化率，其中以硼氫化鈉還原下的Au-Pd/TiO2觸媒達最高的活性，可在反應時間180分鐘達100%的轉化率。經由鑑定結果分析Au-Pd/TiO2觸媒經過還原可降低金的氧化態增加反應活性基點且硼的氧化物可以保護金顆粒避免氧化。表示利用金觸媒的良好選擇性與鈀觸媒高轉化率可以有效提高觸媒應用性。 Nanosized gold catalyst has been reported to be a good catalyst for the liquid phase hydrogenation reactions due to their excellent activity and selectivity. In this research, two investigations were carried out on the gold catalyst: the affection of cobalt oxides and palladium to gold catalysts. A series of Au catalysts supported on CoOx-TiO2 with various Co contents were prepared. CoOx-TiO2 support was prepared by incipient-wetness impregnation with aqueous solution of Co(NO3)2 on TiO2. Gold catalysts were prepared by deposition-precipitation method (DP) with 1 wt. % Au loading. The molar rations of Co to Ti were 0, 1/99, 6/94, 1/9, 2/8, 3/7 and 1.0, respectively. The catalysts were denoted as Au/CoOx-TiO2 (m), where m represented the atomic ratio of Co/Ti. Palladium was added as a second metal on TiO2 which were prepared by impregnation with aqueous solution of Pd(NO3)2. Gold catalysts were prepared by deposition-precipitation method (DP) with 1 wt. % Au loading. After preparation, the catalysts were reduced under H2 at 423oC for 2h and reduced by sodium borohydride in the methanolic solution (50/50 methanol/water) at 298K under vigorous stirring and used nitrogen stream to remove air. These catalysts were characterized by inductively-coupled-plasma-mass spectrometry (ICP-MS), X–ray diffraction (XRD), transmission electron microscopy(TEM), high resolution transmission electron microscopy(HR-TEM), X-ray photoelectron spectroscopy(XPS) and temperature programmed reduction (TPR). The catalytic properties of gold based catalysts were studied on hydrogenation of p–chloronitrobenzene (p-CNB). The conditions for hydrogenation reaction were 1.2 MPa H2 pressure, 353 K reaction temperature and 500 rpm stirring speed. Methanol was used as the solvent, the concentration of p-CNB was 0.2 M (2.54g p–CNB in 80 ml methanol) and the amount of gold based catalyst was 0.5g. The cobalt oxide in Au/CoOx-TiO2 plays the role of a textural promoter, prevents from sintering of gold particle, increased active sites, and then enhanced catalytic activity. Cobalt not only good in steric effect, but also be an electronic promoter, which donated partial electronic to Au. Au/CoOx-TiO2 (1:9) exhibited the highest activity among the series of Au/CoOx-TiO2. The Au-Pd/TiO2 catalyst which reduced by NaBH4 could reached 100% conversion at 180 min reaction time. The results showed that NaBH4 reduction could prevent Au0 from being oxidized, increased the active site. It could be concluded that suitable cobalt amount shows the best performance, and palladium could promote the conversion effectively. |
