改質鎳硼觸媒於對氯硝基苯氫化反應的應用

The applications of modified NiB catalysts on the hydrogenation of p-chloronitrobenzene

林明宏(Ming-Hung Lin)

指導教授 ： 陳郁文

國立中央大學/工學院/化學工程與材料工程學系/碩士(2008年)

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、醋酸鈷和添加劑(鉬、鑭、鐵和鵭)為前驅鹽類，以化學還原法製備改質後的非晶相鎳硼和鎳鈷硼合金觸媒，製備條件為：鎳/鈷/硼之莫耳比為1:0.1:3，鎳/添加劑之莫耳比為1:0.1，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(298K)；攪拌速率為500rpm；製備溶劑使用50 vol%甲醇之混合溶劑；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，以氮氣吸附儀、X–光繞射儀、穿透式電子顯微鏡和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353K；壓力為1.2MPa (160psi)；攪拌速率500rpm；反應溶劑為80ml甲醇；每十分鐘取樣品一次，打入氣相層析儀中分析，結果顯示添加劑的加入，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，對主產物對-氯苯胺的選擇率皆大於90%。
鐵改質後的鎳硼觸媒以NiFeB (1:0.1)的活性最佳，選擇性亦提升很多；改質後的鎳鈷硼觸媒，以Mo-NiCoB (0.1:1:0.1)和W-NiCoB (0.1:1:0.1)的電子轉移較明顯，致使氫化活性最好、選擇性最佳；針對鉬改質後的鎳鈷硼觸媒擁有較好的活性與選擇性，探討鉬/鎳不同的莫耳比，發現Mo-NiCoB (0.6:1:0.1)觸媒的氫化活性極佳，10分鐘內即達到100%的轉化率，98%的選擇率。
討論改質後的觸媒之特性，利用X–光繞射儀之圖譜說明金屬鹽類在還原後形成合金形態，探討著其中的電子轉移，更闡明粒子大小與添加劑的關係，添加劑使得觸媒的表面積變大，粒徑變小且以奈米級的大小存在。

關鍵字

非晶相鎳合金觸媒 ； 液相氫化反應 ； 奈米級 ； 添加劑

並列摘要

Amorphous NiB alloy catalysts are beneficial for the hydrogenation of p-chloronitrobenzene (p-CNB). 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, cobalt acetate and additives (Mo, La, Fe and W), and prepared a series of modified Ni-B and NiCoB catalysts by chemical reduction method. The molar ratio of Ni/Co/B and Ni/additive was relatively 1:0.1:3 and 1:0.1, respectively, 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. In order to analyze the physical, chemical and surface properties, the as-prepared catalysts were characterized by nitrogen sorption (BET), X–ray diffraction (XRD), transmission electron microscopy (TEM) and X–ray photoelectron spectroscopy (XPS). The activity and selectivity of catalysts were tested for the liquid-phase hydrogenation reaction of p-CNB at 353 K and 1.2MPa H2 pressure under vigorous stirring of 500 rpm in a 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 chromatograph. The results revealed that adding the additives into the catalysts would enhance the thermal stability, dispersing effect of active sites, activity and selectivity. The selectivity of main product, p-chloroaniline (p-CAN) was more than 90%.
The results of the reaction showed that the performance of the modified NiFeB (1:0.1) was the best one between a series of Fe-doped NiB catalysts and the selectivity also increased significantly. For modified NiCoB catalysts, Mo- and W-doped ones were better than the other catalysts, and more obvious electron transfer contributed to the best activity and selectivity. In order to study the influence of Mo/Ni molar ratio on the catalytic activity of Mo-doped NiCoB catalysts, the molar ratio of Mo/Ni was modified and found that the Mo-NiCoB (0.6:1:0.1) catalyst had excellent hydrogenation activity. It achieved 100% conversion within 10 min with a selectivity of 98%.
In order to discuss the characterization of modified catalysts, the XRD patterns confirmed the formation of alloy. All the metals would form alloy and hence the major focus was on the phenomenon of electron transfer. Furthermore, the relationship between the particle size and additives was correlated. The particle size would decrease and the surface area would increase with the introduction of the additives. Therefore, the catalysts were in nano-scale range as confirmed from the TEM images and BET measurement.

並列關鍵字

amorphous Ni alloy catalyst ； NiCoB ； additive ； liquid-phase hydrogenation ； modified catalysts

參考文獻

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