Magnetic nano-structured cobalt–cobalt oxide/nitrogen-doped carbon material as an efficient catalyst for aerobic oxidation of p -cresols

Efficient aerobic oxidation has been developed for the selective preparation of a sequence of valuable p-hydroxybenzaldehydes from corresponding p-cresols, using a new magnetically separable catalyst of nano-structured cobalt–cobalt oxide/nitrogen-doped carbon (CoOx@CN) material. CoOx@CN showed high activity for the 2-methoxy-4-cresol oxidation to vanillin, giving great yield (90%) and with good turnover number (210), as well as other p-cresols in good to great yields. The catalytic performance was investigated and related to the structural, chemical and magnetic properties which determined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FT-IR) and vibrating sample magnetometer (VSM). The effects of base to substrate molar ratio, catalyst concentration, temperature, and solvent on the conversion and selectivity patterns also have been studied. The investigation revealed that remarkable catalytic properties of CoOx@CN could be ascribed to the active species cobalt oxide, doped nitrogen and porous carbon with large surface area. The size of the catalyst is a key factor for catalyst performance. The ferromagnetic property of catalyst enables to recycle easily by an external magnetic field and reuse six successive times without significant activity loss.