Issue 11, 2020

Selective synthesis of α-olefins by dehydration of fatty alcohols over alumina–thoria mixed catalysts

Abstract

The selective and high-yield production of α-olefins by alcohol dehydration is challenging because the isomerization and polymerization olefin products are more thermodynamically stable. In this study, we prepared a physical mixture of nano-sized alumina (Al2O3n) and thoria (ThO2) with high efficiency and selectivity towards the production of α-olefins from stearic alcohol (100% conversion, 92% yield of α-olefin, rate: 2.925 mmol g−1 h−1, solvent: dodecane, 300 °C). To the best of our knowledge, this is the most efficient system developed for fatty α-olefin production from fatty alcohols, as compared to literature. Dehydration experiments of cis- and trans-2-methyl cyclohexanol over Al2O3n revealed the reaction to proceed by anti-elimination, which was favored by the abundance of Lewis acidic sites (LAS, 0.457 mmol g−1) and Lewis basic sites (LBS, 0.567 mmol g−1) on the porous surface of Al2O3n. LAS adsorbed and eliminated the hydroxyl groups (–OH) of stearic alcohol, generating a carbonium ion (carbocation) intermediate, which was subsequently, converted to the alkene as final products over the LBS. However, the selectivity and yield of α-olefin were comparatively low over pure Al2O3n due to the formation of isomeric olefin products. Interestingly, the addition of ThO2 increased yield of α-olefin up to 92% owing to the strong adsorption of this compound on the catalytic surface at high temperatures (300 °C), as evidenced by in situ Fourier transform infrared spectroscopy (FTIR)-ethylene adsorption analyses. Consequently, ThO2 hindered the undesired isomerization and oligomerization of α-olefin taking place over LAS, thereby enhancing the yield of α-olefin products.

Graphical abstract: Selective synthesis of α-olefins by dehydration of fatty alcohols over alumina–thoria mixed catalysts

Supplementary files

Article information

Article type
Paper
Submitted
19 Mar 2020
Accepted
06 May 2020
First published
07 May 2020

Catal. Sci. Technol., 2020,10, 3701-3708

Selective synthesis of α-olefins by dehydration of fatty alcohols over alumina–thoria mixed catalysts

A. Ali and C. Zhao, Catal. Sci. Technol., 2020, 10, 3701 DOI: 10.1039/D0CY00551G

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