Construction of multifunctional lanthanum manganese mixed nanoparticles mediated by ionic liquids for selective aerobic oxidation of cyclohexane

Selective oxidation of alkanes to produce high-value chemicals is an essential strategy and means to realize efficient utilization of resources. In this work, a strategy of lanthanum manganese mixed metal oxides (LMMO) regulated via a facile ionic liquid (IL)-assisted hydrothermal method was proposed to construct the multifunctional catalysts, which exhibited excellent catalytic performance in the selective aerobic oxidation of cyclohexane. An 8.9% cyclohexane conversion with 90% KA oil (cyclohexanol and cyclohexanone) selectivity was achieved over the optimal LMMO catalyst under mild conditions. The effects of anion type, carbon chain length and concentration of ILs on the structure and properties of catalysts were investigated through various characterizations, indicating the structure-directing and template effect of ILs on the multifunctional catalysts. The formation of self-assembled spherical nanoparticles followed the “dissolution-nucleation-proliferation” mechanism with the introduction of 1-butyl-3-methylimidazolium hydrogen sulfate, ascribing the synergistic effect between the microenvironment of ILs and the hydrothermal environment. Importantly, the high reactive oxygen concentration, redox capacity, and suitable basic sites of LMMO catalysts mediated by ILs enhance the activation of C-H bonds and molecular oxygen, simultaneously influencing the adsorption and desorption of the substrate. A comprehensive understanding of the high KA oil selectivity and radical reaction mechanism was elucidated based on in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and radical trapping experiments. The recycling and regeneration experiments further illuminated that the removal of adsorbed cyclohexanone acting on the LMMO catalyst was the key to achieve high KA oil selectivity. Graphical abstract