MnO₂ nanorod supported gold nanoparticles with enhanced activity for solvent-free aerobic alcohol oxidation

Gold nanoparticles supported on β-MnO₂ with different morphologies, i.e., nanorods and conventional particulates, were prepared by homogeneous deposition-precipitation using urea as the precipitation agent. The catalysts were extensively characterized by a combination of different techniques (N₂ adsorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), hydrogen temperature-programmed reduction (H ₂-TPR), and X-ray photoelectron spectroscopy (XPS)) in relation to their performance for liquid-phase aerobic oxidation of benzyl alcohol under solvent-free conditions. TEM analysis showed that the two types of gold catalysts have similar gold particle size distributions. TPR results indicated that the presence of Au strongly promotes MnO₂ reduction in the Au/MnO₂-R system. XPS revealed both reduced and oxidized Au species on the MnO₂ nanorods support before and after the reaction. Significantly enhanced catalytic activity was observed for gold catalyst supported on MnO₂ nanorods, as compared with that on commercial MnO₂ powders. The enhanced catalytic activity of the Au/MnO ₂-R catalyst was attributed to the beneficial presence of higher amount of oxidized gold species and surface oxygen vacancies resulting from the strong interaction between Au and the well-defined reactive surface of MnO ₂ nanorods.