Catalytic Effect of Magnetic Nanoparticles Over the H₂O₂ Decomposition Reaction

This paper compares the rate of decomposition of hydrogen peroxide when controlled nano-sized magnetite powders are used as catalysts. Two different nano-sized powders and a Fe⁰/Fe₃O₄ composite have been used. The nanoparticle samples were synthesized by: (i) a chemical reduction–precipitation method and, (ii) by reduction under H₂ atmosphere at 250 °C, of a hematite sample previously prepared. The composite, Fe⁰/Fe₃O₄, was prepared by thermal controlled reduction of nanoparticles of Fe₂O₃ obtained from hematite under H₂ at 300 °C. The samples were characterized by Fourier-transform infrared, X-ray diffraction, and Mössbauer spectroscopy at room temperature, and surface area. The catalytic effect was studied in the decomposition reaction of H₂O₂ by measuring the formation of gaseous O₂. The results showed the presence of pure Fe₃O₄ for nano magnetite samples and Fe⁰ and Fe₃O₄ for the composite sample. The average particle sizes of the magnetite, calculated from reflection 311 by using Scherrer equation were about 33 and 10 nm for the samples obtained by hematite reduction and reduction–precipitation, respectively. Kinetic studies of the decomposition of peroxide showed a higher decomposition rate for the hydrogen peroxide reaction when nanoparticles prepared by reduction–precipitation method were used as catalysts. The high catalytic activity associated to nanoparticles is discussed in terms of the high surface area of these samples.