Reduction of carbon dioxide into carbon by freshly reduced CoFe_2O_4 nanoparticles

摘要

The reduction of one of the greenhouse gases, CO_2, has been a current subject in the field of environmental chemistry. Cobalt ferrite nanoparticles with different sizes were prepared by the thermal decomposition of acetate precursors and wet method techniques. CoFe_2O_4 nanoparticles were compacted, then isothermally reduced in H_2 flow at 400-600℃. The isothermal reduction profiles obtained show that a topochemical mode of reduction is developed as the process proceeds. The metallic phases of iron and cobalt, produced from the complete reduction of CoFe_2O_4 are in nanosize form. The prepared, completely reduced and reoxidized CoFe_2O_4 compacts were characterized by XRD, SEM and reflected light microscope. The reoxidation process is affected by both particle size and reoxidation temperature. At the initial stages, the reaction was controlled by the interfacial chemical reaction mechanism with some contribution of the gaseous diffusion mechanism. On the other hand, at the final stages the mechanism by which the reoxidation process proceeds was found to be the solid-state diffusion. CO_2 decomposes on the surface of metallic phases with 99% conversion at 550℃ to form single- and multi-walled carbon nanotubes.