Water-promoted selective hydrogenation of cinnamaldehyde over hydrotalcite-derived Co catalysts

Non-noble metal-catalyzed selective C[dbnd]O hydrogenation of α,β-unsaturated aldehydes to corresponding alcohols is chemically atom economic and practically feasible. This work reports hydrotalcite-derived Co-based catalysts for catalyzing aqueous phase selective hydrogenation reaction of cinnamaldehyde to cinnamyl alcohol. The structure characterizations demonstrate the phase transition from hydrotalcite to co-existed CoO_x and metallic Co⁰ in the optimal Co₂Al-H₂-400 catalyst. It exhibits superior catalytic activity and selectivity relative to other as-obtained Co catalysts, because of the synergy effect of Co²⁺ sites to promote the adsorptive activation of C[dbnd]O group and small-size Co⁰ sites to facilitate the activating dissociation of hydrogen. Furthermore, the catalytic role of water has also been explored. Adopting water as pure solvent and partially adding water into organic solvent can both effectively enhance the activity and selectivity. Such reaction environment may induce creation of more intermolecular hydrogen bonds for promoting the hydrogen transfer and thus boosting the hydrogenation reaction.