非晶形奈米鎳合金觸媒的製備及其 在對-氯硝基苯液相選擇性氫化反應之研究

Preparation of Amorphous Nano-sized Nickel alloy Catalysts and its Application for Liquid Phase Selectivity p-Chloronitrobenzene Hydrogenation Reaction

劉玉章(Yu-Chang Liu)

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/博士(2005年)

摘要

本論文探討用硼氫化鈉為還原劑、醋酸鎳為前驅鹽類跟次磷酸鈉，以化學還原法製備NiB跟NiPB奈米合金觸媒，藉由ICP、BET、XRD、TEM及XPS等儀器瞭解其物理與表面性質，再以對-氯硝基苯(p-CNB)之液相氫化反應，瞭解NiB奈米合金系列觸媒的催化性質與氫化活性，並與商用鎳–鋁觸媒倫尼鎳(Raney Nickel)之活性做比較。NiB觸媒之最佳製備條件為：鎳/硼莫耳比為1/3，298K製備溫度，通氮氣流，攪拌速率500rpm，可在短時間內製得具有活性之新鮮鎳觸媒。添加促進劑(鈷、鑭等)能提升結晶溫度增加觸媒熱穩定性，並增加觸媒分散度，促進劑金屬大都集中於觸媒表層，並與硼相同有供給電子的能力，提高活性。高分子穩定劑PVP，分子量以10k為主，添加量PVP/Ni莫耳比10為較佳製備觸媒比例，結果顯示能有效降低觸媒粒徑，並為耐熱性與結構穩定性較佳的非晶形奈米合金觸媒。 奈米鎳觸媒以液相選擇性對-氯硝基苯氫化反應測試其活性，反應條件同樣能提升氫化反應的活性，使用甲醇當溶劑為反應媒介比乙醇能大範圍的提升對-氯硝基苯的轉化率。所有NiB觸媒系列的主產物對-氯苯胺(p-CAN)其選擇率都大於99%。

關鍵字

液相氫化反應 ； 鎳 ； 奈米觸媒 ； 對-氯硝基苯的氫化反應

並列摘要

A series of NiB catalysts were prepared by mixing nickel acetate in 50% ethanol /water or methanol/water solution. The solution of sodium borohydride (1 M) in excess amount to nickel was then added dropwise into the mixture to ensure full reduction of nickel cations. The mol ratio of boron to nickel in mother solution was 3
to 1.
A series of Ni-P-B catalysts were prepared by liquid phase reduction. Nickel acetate and sodium hypophosphite were mixed in ethanolic solution. The solution of sodium borohydride in excess amount was then added dropwise into the above mixture to ensure full reduction of nickel cations. The Ni:P:B ratios in the mother
solution was used 1:3:3 and 1:1:3.
A promoter of lanthanum and cobalt metals was addition to NiB catalysts. The La- NiB catalyst was passivity by boron; therefore it was more stable than Raney nickel and did not catch fire after exposure to air.
The effects of preparation conditions such as temperature, stirring speed, and sheltering gas on the particle size, surface compositions, electronic states of surafce atoms and catalytic activities of the NiB catalysts were studied. Ranel nickel catalyst was included for comparison. These catalysts were characterized by Inductively coupled plasma atomic emission spectroscopy, N2 sorption, X-ray diffraction, trnasmission electron microscopy, and X-ray photoelectron spectroscopy. The catalysts were tested for liquid phase hydrogenation of p-chloronitrobenzene. All of the catalysts prepared in this study had nanosized particles. The preparation condition has significant influence on the particle size and surface compositions of the catalyst. The NiB catalyst was passivity by boron; therefore it was more stable than Raney nickel and did not catch fire after exposure to air. The catalysts prepared under N2 flow could suppress the oxidation of Ni by the dissolved oxygen in water and had metallic state of nickel. The catalyst prepared with vigorous stirring at 25oC under N2 stream yielded the smallest particles and resulted in the highest activity. It was much
more active than the Raney nickel catalyst.
The reaction condition also has pronounced effect on the hydrogenation activity. Using methanol as the reaction solvent increased p-chloronitrobenzene conversion to a large extent, compared to that using ethanol as the reaction medium. The selectivity of main product (p-chloroaniline) was greater than 99 % on all of the NiB catalysts.

並列關鍵字

nanocatalyst ； nickel ； liquid phase hydrogenation ； hydrogenation of

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