Selective Hydrogenation of Cinnamaldehyde over Co/γ-Al_2O_3 Catalysts──Characterization of the Catalysts

Supported Co/γ-Al2O3 catalysts for cinnamaldehyde hydrogenation wcre prepared by impregnation from different precursors, Co (No3), and CoCl2, which were designated by the names of catalyst A and catalyst B.These catalysts were investigated using XRD, TPR and XPS techniques' Co3O4 phase was detected by XRD before reduction, and α-Co phase in both catalysts after reduction by hydrogen. As far as the phase structure of active cobalt was concerned, there was no difference between the catalysts prepared from different precursors.TPR results indicated that there are two species of Co3Co4on the support, namely, crystal1ine form and dispersed form. However, XPS revealed that the amount of Co0 in catalyst A is less than that in catalyst B after reduction. The results implied a stronger interaction between cobalt and γ-Al2O3 support in catalyst A, which is not advantageous to the hydrogenation of carbonyl group. Due to the introdUction of K+ from KOH precipitant, the activity of catalyst B is higher than catalyst A. The cobalt particles are larger after reduction, which is advantageous to selectivity. The combination of K+ and Cl- in catalyst B tesults in higher selectivity in hydrogenation of cinnamaldehyde to cinnamyl alcohol.