Heterogeneous Ni Catalysts for N-Alkylation of Amines with Alcohols

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• 作者：Ken-ichi Shimizu ; Naomichi Imaiida ; Kenichi Kon ; S. M. A. Hakim Siddiki ; Atsushi Satsuma
• 刊名：ACS Catalysis
• 出版年：2013
• 出版时间：May 3, 2013
• 年：2013
• 卷：3
• 期：5
• 页码：998-1005
• 全文大小：399K
• 年卷期：v.3,no.5(May 3, 2013)
• ISSN：2155-5435

文摘

Nickel nanoparticles loaded onto various supports (Ni/MO_x) have been prepared and studied for the N-alkylation of amines with alcohols. Among the catalysts, Ni/胃-Al₂O₃ prepared by in situ H₂-reduction of NiO/胃-Al₂O₃ shows the highest activity, and it acts as reusable heterogeneous catalyst for the alkylation of anilines and aliphatic amines with various alcohols (benzyl and aliphatic alcohols) under additive free conditions. Primary amines are converted into secondary amines and secondary amines into tertiary amines. For the reaction of aniline with an aliphatic alcohol the catalyst shows higher turnover number (TON) than precious metal-based state-of-the-art catalysts. Mechanistic studies suggest that the reaction proceeds through a hydrogen-borrowing mechanism. The activity of Ni catalysts depends on the nature of support materials; acid鈥揵ase bifunctional supports give higher activity than basic or acidic supports, indicating that acid鈥揵ase sites on supports are necessary. The presence of basic (pyridine) or acidic (acetic acid) additive in the solution decreased the activity of Ni/胃-Al₂O₃, which suggests the cooperation of the acid鈥揵ase site of 胃-Al₂O₃. For a series of Ni/胃-Al₂O₃ catalysts with different particle size, the turnover frequency (TOF) per surface Ni increases with decreasing Ni mean particle size, indicating that low-coordinated Ni species and/or metal鈥搒upport interface are active sites. From these results, we propose that the active site for this reaction is metal鈥搒upport interface, where low-coordinated Ni⁰ atoms are adjacent to the acid鈥揵ase sites of alumina.

Keywords:

alcohols; amines; heterogeneous catalysis; nickel; nanoparticles