Porous Ru/RuOx/LDH as highly active heterogeneous catalysts for the aerobic oxidation of alcohols

Abstract

Deposition of pre-preparation nanocatalysts onto catalyst supports with good particle dispersion and stability is still a great challenge in the field of heterogeneous catalysis. In this work, a bottom-up self-assembly route was developed to construct porous Ni²⁺–Al³⁺ layered double hydroxide (LDH) supported Ru/RuO_x nanocatalysts without the usage of surfactants. The obtained catalysts exhibited much better catalytic activity and stability than conventional Ru-based catalysts for the aerobic oxidation of alcohols under mild conditions. This is mainly due to their hierarchical porous structure which facilitates the diffusion of reactants and products, and the high dispersion of accessible catalytic Ru nanoparticles. Furthermore, the activities of Ru/LDH nanocatalysts could be enhanced by adjusting the ratios between Ni²⁺ and Al³⁺ in LDH nanosheets. After careful investigation of surface chemical properties by X-ray photoelectron spectroscopy (XPS), it was found that the high catalytic activity of Ru-based catalysts for the aerobic oxidation of alcohols was mostly contributed by RuO_x species on the surface of Ru nanoparticles, but not Ru⁰. These findings opened up another avenue to develop high-performance Ru based heterogeneous catalysts for the aerobic oxidation of alcohols.