A facile synthesis of in-situ formed amorphous zirconia catalysts for efficient transfer hydrogenation of unsaturated aldehydes

Several metal salts were used for the cinnamaldehyde transfer hydrogenation, and it was found that heterogeneous reactions coexisted in this superficial homogeneous catalytic system. Among these metal salts, Zr(NO3)4·5H2O exhibits the best catalytic performance. Notably, the in-situ formed amorphous zirconia during the reaction is identified as the active site of Zr(NO3)4·5H2O. The in-situ formed zirconia in the presence of cinnamaldehyde (self-selective ZrO2) possesses smaller particle size, better dispersion and more surface hydroxyl groups, which exhibits remarkably enhanced catalytic performance in cinnamaldehyde transfer hydrogenation as compared to the commercial nano-zirconia and laboratory-prepared zirconia. The characterization and theoretical analysis reveal that the synergistic catalytic effect between zirconium active site and surface hydroxyl groups can effectively activate CO bonds in cinnamaldehyde and reduce the activation energy barrier, thus significantly improving the transfer hydrogenation performance. Moreover, the self-selective ZrO2 exhibits excellent catalytic performance for a series of unsaturated aldehydes.