Novel Synthesis and Characterization Studies of Spinel Ni _x Co_1−x Al₂O₄ (x = 0.0 to 1.0) Nano-Catalysts for the Catalytic Oxidation of Benzyl Alcohol

Ni-doped cobalt aluminate Ni _x Co_1−x Al₂O₄ (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) spinel nanoparticles were successfully synthesized by a simple microwave combustion method using urea as the fuel and as well as reducing agent. X-ray powder diffraction (XRD) was confirmed the formation of single phase, cubic spinel cobalt-nickel aluminate structure without any other impurities. Average crystallite sizes of the samples were found to be in the range of 18.93 nm to 21.47 nm by Scherrer’s formula. Fourier transform infrared (FT-IR) spectral analysis was confirmed the corresponding functional groups of the M–O, Al–O and M–Al–O (M = Co and Ni) bonds of spinel Ni _x Co_1−x Al₂O₄ structure. Scanning electron microscope (SEM) and transmission electron microscope (TEM) images was confirmed the particle like nanostructured morphology. Energy band gap (E _g) value was calculated using UV-Visible diffuse reflectance spectra (DRS) and the E _g values increased with increasing Ni²⁺ dopant from x = 0.2 (3.58 eV) to x = 1.0 (4.15 eV). Vibrating sample magnetometer (VSM) measurements exposed that undoped and Ni-doped CoAl₂O₄ samples have superparamagnetic behavior and the magnetization (M _s) values were increased with increasing Ni²⁺ ions. Spinel Ni _x Co_1−x Al₂O₄ samples has been used for the catalytic oxidation of benzyl alcohol into benzaldehyde and was found that the sample Ni_0.6Co_0.4Al₂O₄ showed higher conversion 94.37% with 100% selectivity than other samples, which may be due to the smaller particle size and higher surface area.