Green and Selective Oxidation of Benzyl Alcohol to Benzaldehyde over Transition Metal LDH Nanosheets: Combining Experiments and DFT Calculations

The solvent-free and aerobic oxidation of benzyl alcohol is an exceptionally efficient approach for synthesizing benzaldehyde; however, the conversion rates and selectivity are still insufficient as effective catalysts need to successfully activate both the O-H bond and the O₂ molecules. In this study, various layered double hydroxides (LDHs) were successfully prepared and employed for the oxidation of benzyl alcohol in a solvent-free environment. The specific LDHs employed in this study comprise Cu-Co-Fe-LDH (I), Zn-Co-Fe-LDH (II), Zn-Ni-Co-Fe-LDH (III), and Cu-Ni-Co-Fe-LDH (IV). The presence of LDH structures in all analyzed samples was verified through X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), along with additional techniques such as Raman spectroscopy, scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). The Cu-Ni-Co-Fe-LDH catalyst exhibited excellent activity in solvent-free benzyl alcohol oxidation, achieving conversions of 7.47% and 12.34% after 5 h, with benzaldehyde selectivity above 99% and 92% under atmospheric and 10 atm O₂, respectively. Density functional theory (DFT) calculations demonstrated that alloying the surface of Cu-Ni-Co-Fe-LDH may stabilize important intermediate adsorbates in the conversion of ph-CH₂OH to ph-CHO. These catalysts show great potential for the selective conversion of benzyl alcohol into valuable products for chemical and petrochemical applications.