Preparation of Ni/CuO/MCM-41 for indole oxidation: optimisation processes

In this study, several catalysts – namely, MCM-41, copper (II) oxide (CuO), copper (II) oxide/MCM-41, nickel (Ni)/copper (II) oxide and nickel/copper (II) oxide/MCM-41 – were synthesised and characterised by way of X-ray diffraction, Fourier transform infrared spectroscopy, field-emission scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy and Brunauer–Emmett–Teller/Barrett–Joyner–Halenda techniques. The oxidation of indole (C₈H₇N) by these synthesised catalysts was evaluated at room temperature by using an ultraviolet spectrophotometer. It was revealed that adding nickel to copper (II) oxide/MCM-41, even at low concentrations, significantly increased the oxidation efficiency. Furthermore, to obtain the optimal operating conditions, the influences of the weight percentage of nickel, pH, the mass of catalyst and contact time, each at three levels, on indole oxidation were studied by applying the response surface methodology based on the Box–Behnken design method. The obtained results indicated that pH and nickel weight percentage were the most critical factors. Finally, although several kinetic models were applied for investigating the kinetic mechanism of indole oxidation by way of the nickel/copper (II) oxide/MCM-41 composite, the most suitable model for this purpose was the Blanchard kinetic model.