Multilayer Nb₂CT_x (MXene) Supports CoB for the Selective Hydrogenation of Cinnamaldehyde to Cinnamyl Alcohol: Effect of the Electron-Modified CoB Site and Lewis Acid Site

A heterogeneous CoB/Nb₂CT_x catalyst was successfully prepared by in situ wet reduction of Co metal ions electrostatically adsorbed on the surface of Nb₂CT_x and applied to the selective hydrogenation of cinnamaldehyde (CAL). The 10 wt% CoB/Nb₂CT_x catalyst exhibited superior catalytic activity with a CAL conversion of 90.4% and a cinnamyl alcohol (COL) selectivity of 75.4%, while unsupported CoB showed a CAL conversion of only 24%. The characterization results showed that CoB was dispersed on the surface and in the Nb₂CT_x layers, and CoB/Nb₂CT_x exposed more effective active sites than CoB alone, leading to higher hydrogenation activities. In addition, the transfer of electrons from B to Co increased the electron density of Co, which rejects the adsorption on the C=C bond. A strong electronic effect existed between the dispersed surface CoB and Nb₂CT_x, and B contributed electrons to Nb₂CT_x, resulting in the formation of more electron-deficient B species, which serve as electrophilic sites for C=O adsorption. Moreover, Lewis acid sites on the surface of Nb₂CT_x were conducive to the adsorption of C=O bonds. The electron-deficient B and the Lewis acid site on the surface of CoB/Nb₂CT_x promoted the adsorption of C=O, resulting in a high yield of COL from CoB/Nb₂CT_x.