Selective hydrogenation of stearic acid to stearyl alcohol over cobalt alumina catalysts

Highlights

• Co/Al₂O₃ selectively converts stearic acid to stearyl alcohol at 300 °C & 50 bar H₂.

• Selective hydrodeoxygenation occurs over metallic Co.

• Lewis acidity from support results in the formation of esters.

• Higher Co loading reduces Lewis acidity from the support improving selectivity.

Abstract

The selective hydrogenation of stearic acid to produce stearyl alcohol at 300 °C and 50 bar pressure was studied over a series of cobalt alumina catalysts with different cobalt loadings. Catalysts were prepared by wet impregnation and characterised by X-ray diffraction, H₂ temperature programmed reduction, H₂ chemisorption, N₂ adsorption-desorption and Fourier-transform infrared spectroscopy. Stearyl alcohol was observed to be the main reaction product, although heptadecane, octadecane and stearyl stearate were also produced in lesser amounts. The product selectivity was influenced by the availability of Lewis acid sites on the support which were found to be responsible for ester formation. Increasing the cobalt loading diminished the number of acid sites on the support surface whilst increasing the number of cobalt metal sites and thus enhanced the relative rate of hydrogenation leading to improved selectivity to stearyl alcohol.