Defect Engineering in Pd/NiCo₂O_4–<i>x</i> for Selective Hydrogenation of α,β-Unsaturated Carbonyl Compounds under Ambient Conditions

Abstract

The highly selective hydrogenation of α,β-unsaturated carbonyl compounds is challenging and desirable in pharmaceutical manufacturing. Moreover, the ability to activate specific functional groups in complex starting materials is also in line with the concept of sustainable chemistry. Here, we use a simple room temperature chemical reduction strategy to implant defects into NiCo2O4 while loading metal Pd. The synthesized Pd/NiCo2O4–x shows good catalytic performance for the selective (nearly 100%) hydrogenation of cinnamaldehyde to hydrocinnamaldehyde under mild conditions. Furthermore, the selectivity to hydrocinnamaldehyde can still be maintained by extending the reaction time and increasing the reaction temperature. Density functional theory calculations indicated that the C═C bond of cinnamaldehyde is preferentially adsorbed on the surface of Pd nanoparticles than the C═O bond. After hydrogenation of cinnamaldehyde to hydrocinnamaldehyde, the C═O bonds of hydrocinnamaldehyde are strongly adsorbed by the oxygen defect of the NiCo2O4–x. The adsorbed hydrocinnamaldehyde on oxygen defects will be erected on the surface of NiCo2O4–x, which can impede the adsorption of hydrocinnamaldehyde on Pd nanoparticles. So, the further hydrogenation of hydrocinnamaldehyde is hindered. The present work provide new insights into highly selective hydrogenation of α,β-unsaturated carbonyl compounds and paves a new way for the defect engineering to design efficient catalytic materials and beyond.