Liquid phase oxidation of cinnamyl alcohol to cinnamaldehyde using multiwall carbon nanotubes decorated with zinc-manganese oxide nanoparticles

Zinc-manganese (Zn-Mn) oxide nanoparticles were prepared and loaded on functionalized multiwall carbon nanotubes (FMWCNTs) (Zn-Mn oxide/FMWCNT) using co-precipitation and developing condensation methods, respectively. The Zn-Mn oxide and Zn-Mn oxide/FMWCNTs were characterized using scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX), x-ray diffraction (XRD), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FT-IR). The catalytic efficiencies of the prepared catalysts were tested for liquid phase oxidation of cinnamyl alcohol (CnOH) to cinnamaldehyde (CnHO) in a modified batch reactor. The reaction parameters were optimized and compared in green (water and heptane), blue (toluene, acetonitrile, and cyclohexane), and red (benzene) solvents and molecular oxygen. The maximum CnOH-to-CnHO conversion of 97.2 and 99.9% with productivity of 63.2 and 65 mmol g⁻¹ h⁻¹ was achieved with 0.1 g of each Zn-Mn oxide and Zn-Mn oxide/FMWCNT, respectively in water at 60 °C and time = 120 min. Both catalysts showed high conversion, high productivity, low cost, recyclability, and true heterogeneous behavior and therefore, can be used effectively for the conversion of CnOH-to-CnHO.