Catalytic conversion of hexanol to 2-butyl-octanol through the Guerbet reaction

Activity of heterogeneous catalysts for synthesis of Guerbet alcohols from hexanol was evaluated. Commercial synthetic hydrotalcite (HT) was used in the aldol condensation reaction, which is a part of the Guerbet reaction network. HTs were calcined at different temperatures in order to modify their basicity and additionally, NaOH was applied in some experiments as a homogeneous base. The homogeneous base proved to be more efficient in aldol condensation experiments, while HT also performed in an acceptable way. Bi-functional metal containing HTs were synthesized by wet impregnation and co-precipitation methods employing different active metals. The materials were characterized with a number of methods, including CO2-TPD, pyridine-FTIR, nitrogen physisorption, transmission electron microscopy, SEM–EDX and XRD. Copper containing catalysts produced hexyl-hexanoate with a very high selectivity, while Ni-containing counterparts exhibited the highest selectivity towards the Guerbet alcohol. The co-precipitated catalysts were more active in the current study than the ones produced by wet-impregnation. Nevertheless, synthesis of Guerbet alcohols from hexanol with a one-pot method proved to be challenging, with the best yield of the Guerbet product in 24 h being 5%. This is proposed to be largely due to thermodynamic limitations, which was confirmed by calculations of thermodynamics.