| 摘要: | 非晶相鎳硼合金觸媒於對-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，探討以硼氫化鈉為還原劑，利用醋酸鎳、鉬酸銨和添加劑(鈀、鑭、鐵和鈷)為前驅鹽類，以化學還原法製備改質後的非晶相鎳鉬硼觸媒，製備條件為：鎳/鉬/硼/添加劑之莫耳比為1: 0.4: 3: 0.1，過量的硼含量為確保前驅鹽類的完全還原；製備溫度為室溫(298 K)；攪拌速率為500 rpm；製備溶劑使用50 vol.%甲醇之混合水溶液；通以氮氣流下，避免製備過程中，觸媒被溶氧所氧化，而使活性降低；故而得到具有高度活性的新鮮觸媒，並探討其物理與化學特性於對-氯硝基苯氫化反應上的影響，以感應耦合電漿、X 光繞射儀、穿透式電子顯微鏡、高解析掃描穿透式電子顯微鏡、X 光能譜散佈分析儀和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；以液相選擇性對-氯硝基苯氫化反應測試觸媒之活性與選擇性，反應條件特定在；反應器為半批式反應器(Parr Reactor Model 4842)，反應壓力為1.2 MPa (160 psi)、攪拌速率500 rpm、兩種反應溫度分別為353 K 及333 K、反應溶劑為80 ml 甲醇；每十分鐘取樣品一次，以氣相層析儀分析其組成，結果顯示添加劑的加入，能使觸媒活性位置分散，並提升反應的活性及選擇率，對主產物對-氯苯胺的選擇率皆大於90%。 改質後的鎳鉬硼觸媒，以La-NiMoB 的電子轉移較明顯，致使氫化活性最好、選擇性較最佳；針對鑭改質後的鎳鉬硼觸媒擁有較好的活性及選擇性，探討不同鑭/鎳的莫耳比對觸媒之影響，發現La(0.2)-NiMoB 觸媒的氫化活性極佳，在333 K 時可於60 分鐘內達到100%轉化率及97.5%的選擇率。 Amorphous NiB alloy catalysts are beneficial for the hydrogenation of p-chloronitrobenzene. They possess better catalytic activity and selectivity in the hydrogenation reaction. In this study, we used sodium borohydride to reduce the precursor salts of nickel acetate, ammonium heptamolybdate tetrahydrate and additives (Pd, La, Fe and Co), and prepared a series of modified NiMoB catalyst by chemical reduction method. The molar ratio of Ni/Mo/B/additive was 1: 0.4: 3: 0.1, and an overdose of B was used to completely reduce the precursor salts. Ni catalysts were prepared in 50 vol.% methanolic solution at 298 K under N2 curtain gas with vigorous stirring of 500 rpm. In order to prevent the catalysts from oxidation and deactivation during the preparation, N2 curtain gas was used. The high activity of fresh catalysts was tested for the hydrogenation of p-CNB. The catalysts were characterized by inductively coupled plasma-mass spectrometry (ICP-MS), X–ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), energy dispersive spectrometer (EDS), and X-ray photoelectron spectroscopy (XPS). The activity and selectivity of catalysts were tested for the liquid-phase htdrogenation reaction of p-CNB at 1.2 MPa pressure and two different temperatures, 353 K and 333 K, and under vigorous stirring of 500 rpm in the batch reactor (Parr Reactor Model 4842). The reaction medium was 80 ml methanol. During the run, the samples were withdrawn periodically (10 min) and analyzed by a gas chromatography. The results revealed that adding the additives into the catalysts would enhance the dispersing effect of active sites, activity and selectivity. The selectivity of main product, p-chloroaniline (p-CAN) was more than 90%. For modified NiMoB catalysts, La-doped one was better than the other catalysts, and more obvious electron transfer contributed to the best activity and selectivity. In order to study the influence of La/Ni molar ratio on the catalytic activity of La-doped NiMoB catalysts, the molar ratio of La/Ni was modified and found that the La(0.2)-NiMoB catalyst had excellent hydrogenation activity. It achieved 100% conversion within 60 min at 333 K with selectivity of 97.5%. |
