Synthesis of menthols from citral on Ni/SiO2–Al2O3 catalysts

The one-pot synthesis of menthols from citral was studied on Ni/SiO2–AlO3 catalysts containing 3.6%, 8.8% and 11.4% Ni. The yield of menthols increased with the amount of Ni up to 94% on Ni(11.4%)/SiO2–AlO3, reflecting the diminution of byproducts formation via acid-catalyzed reactions. The sample deactivation was studied by performing two consecutive catalytic tests. Results showed that Ni(11.4%)/SiO2–AlO3 was a stable, active, and highly selective catalyst because it contained the appropriate density and strength of bifunctional acid/Ni0 active sites to efficiently promote the hydrogenation/isomerization pathway involved in the reaction network while avoiding coke formation.

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► One-pot menthol synthesis from citral is efficiently promoted on Ni/SiO2–Al2O3
► Ni(12%)/ SiO2Al3 yields 94% menthols from citral at 343 K and 2026 kPa
► This value is similar to the best yields reported on metal/acid catalysts