Cooperation between the surface hydroxyl groups of the support and organic additives in the highly selective hydrogenation of citral

A Ru/AlO(OH) catalyst was prepared by co-precipitation and characterised by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), thermo-gravimetry (TG), and Fourier transform infrared spectroscopy (FT-IR). Its catalytic performance was tested in the selective hydrogenation of citral. The results showed that the combination of Ru/AlO(OH) and water obviously improved the catalyst activity and its selectivity to geraniol and nerol. Introducing organic additives increased the hydrophilicity of metal particles, which favoured the adsorption of the citral CO bond over the adsorption of the conjugated CC bond, improving the selectivity to and inhibiting the further hydrogenation of geraniol and nerol. The maximum yield of geraniol and nerol (81%) was achieved in water with ethylenediamine as an additive.

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► Hydrogenation selectivity to CO bond of citral over AlO(OH) is enhanced in water.
► Water film formed by action between AlO(OH) and water leads to the selective adsorption of CO bond.
► Modification of diamines to metal sites can further improve the catalyst performance.