Kinetic analysis of catalytic oxidation of methylene blue over γ-Al₂O₃ supported copper nanoparticles

The kinetics of the catalytic oxidation of methylene blue, with hydrogen peroxide was studied under mild conditions. Several copper catalysts were evaluated, with Cu/Li₂O/γ-Al₂O₃ being the most active catalyst. Atomic absorption spectroscopy (AAS), X-ray diffraction spectroscopy (XRD), ligand based chemisorption (LBC), physisorption (BET), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) were used for the characterization of the catalysts, while the oxidative degradations of methylene blue were followed by ultraviolet-visible spectroscopy (UV-vis). Different intermediate species were detected by gas chromatography-mass spectrometry (GC-MS), and the degradation pathway was proposed. The kinetic data obtained could be modeled to the Langmuir-Hinshelwood model; that is both reactants are adsorbed onto the surface of the nanoparticles. The apparent reaction rate could therefore be related to the surface S of the nanoparticles, to the constant k, related to the rate determining steps, and to the adsorption constant K_MB and K_H2O2 of methylene blue and hydrogen peroxide, respectively.