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

Gold nanoparticles supported on beta-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 (N-2 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/MnO2-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 MnO2 nanorods.