One-pot synthesis of menthol from citral over bifunctional Ni modified micro- and mesoporous molecular sieves

In the current work menthol is synthesized in one-pot starting from citral over Ni modified bifunctional micro- and mesoporous molecular sieve catalysts. Ni modified microporous Beta and mesoporous MCM-41 molecular sieves were synthesized using an impregnation method. The catalysts were characterised using XRD, SEM, FTIR and nitrogen adsorption. 15 wt.% Ni-H-Beta catalyst exhibited the selectivity of 70% to four stereoisomers of menthols was achieved at 100% citral conversion. The second best catalyst was 15 wt.% Ni-H-MCM-41 exhibiting 67% selectivity to menthols, whereas below 1 % menthols were formed over Ni/Al₂O₃ catalysts. These results indicated the necessity of bifunctional catalysts in citral transformation to menthols.