Abstract:

Catalytic reduction of α-pinene was achieved in one pot at room temperature using Span as stabilizer, NiCl₂·6H₂O as catalyst precursor, and NaBH₄ as an alternative to the exogenous flammable and explosive hydrogen. In this catalytic system, the effects of Span type, reaction medium, amounts of NaBH₄ and reaction time on the reduction reaction were investigated, and the optimum reaction conditions were obtained as follows: Span-80 as the stabilizer, methanol as the reaction medium, and 0.5 molar equivalent of NaBH₄ (relative to α-pinene) , 5mol% NiCl₂·6H₂O, reaction at room temperature for 5 hours, under which the conversion of α-pinene and the selectivity of cis-pinane reached 98% and 99%, respectively. In addition, the catalyst could be recycled for 3 times. The leaching and morphology of the catalyst during the recycle were studied by ICP-AES and TEM. The results showed that the leaching of Ni during the recycle was only 0.2%. The particle size of the catalyst after one run was about 4.2nm with uniform dispersion. However, after three cycles, the particle size of some Ni nanoparticles became larger due to aggregation, which may be the main reason for the decrease in the catalysis activity. Besides, XPS and a series of poisoning experiments showed that the active species in the catalytic reaction were probably homogeneous in nature, and the in-situ formed nickel nanoparticles may only serve as a “reservoir” of the catalytic species. Compared with the traditional α-pinene hydrogenation process, the proposed process has the advantages of safe, mild, and easy operation and high selectivity.

Key words: α-pinene, reduction, sodium borohydride, Ni nanoparticles, Span-80, cis-pinane

摘要：

以斯盘类表面活性剂为稳定剂，以NiCl₂?6H₂O 为催化剂前体，以NaBH₄替代外源易燃易爆的氢气，在室温条件下于“一锅”中实现了α-蒎烯的催化还原。考察了斯盘类型、反应介质、NaBH₄用量及反应时间对于反应的影响，得到适宜的反应条件为：Span-80为稳定剂，甲醇为反应介质，NaBH₄∶α-蒎烯摩尔比为0.5，5%NiCl₂·6H₂O，室温反应5h，α-蒎烯的转化率可高达98%，顺式蒎烷的选择性达99%，催化剂能循环使用3次。使用ICP-AES及TEM研究了循环过程中催化剂的流失及形貌，结果表明：在循环过程中Ni的流失率仅为0.2％；催化剂运行1次后的粒径约为4.2nm且分散均匀，循环3次后部分Ni纳米粒子的粒径因聚集而变大，这也许是造成催化剂活性降低的主要原因。XPS和一系列中毒实验结果表明，催化反应的活性物种在性质上很可能是均相的，而原位生成的纳米镍粒子也许仅作为催化物种的“储库”。与传统α-蒎烯加氢工艺相比，该工艺的特点是安全、温和、操作性强、选择性高。

关键词: α-蒎烯, 还原, 硼氢化钠, 纳米Ni, 斯盘-80, 顺式蒎烷