One-Pot Transformation of Citronellal to Menthol Over H-Beta Zeolite Supported Ni Catalyst: Effect of Catalyst Support Acidity and Ni Loading

Abstract

Citronellal was converted to menthol in a one-pot approach using H-Beta zeolite-based Ni catalyst in a batch reactor at 80 degrees C, under 20 bar of total pressure. The effects of H-Beta acidity (H-Beta-25 with the molar ratio SiO2/Al2O3 = 25 and H-Beta-300 with SiO2/Al2O3 = 300) and Ni loading (5, 10 and 15 wt %) on the catalytic performance were investigated. Ni was impregnated on H-Beta support using the evaporation-impregnation method. The physico-chemical properties of the catalysts were characterized by XRD, SEM, TEM, ICP-OES, N-2 physisorption, TPR, and pyridine adsorption-desorption FTIR techniques. Activity and selectivity of catalysts were strongly affected by the Bronsted and Lewis acid sites concentration and strength, Ni loading, its particle size and dispersion. A synergetic effect of appropriate acidity and suitable Ni loading in 15 wt.% Ni/H-Beta-25 catalyst led to the best performance giving 36% yield of menthols and 77% stereoselectivity to (+/-)-menthol isomer at 93% citronellal conversion. Moreover, the catalyst was successfully regenerated and reused giving similar activity, selectivity and stereoselectivity to the desired (+/-)-menthol isomer as the fresh one.[GRAPHICS].