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

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