Synthesis and characterization of iron, iron oxide and iron carbide nanostructures

International audienceMagnetic iron oxide (Fe3O4 and γ-Fe2O3) and iron carbide (Fe3C) nanoparticles of different geometrical shapes: cubes, spheres, rods and plates, have been prepared by thermal decomposition of a mixture containing the metal precursor Fe(CO)5 and the stabilizer polyvinylpyrrolidone (PVP) at 300 1C in a sealed cell under inert atmosphere. The thermal decomposition process was performed for 4 or 24 h at ([PVP]/[Fe(CO)5]) (w/v) ratio of 1:1 or 1:5. Elemental iron nanospheres embedded within a mixture of amorphous and graphitic carbon coating were obtained by hydrogen reduction of the prepared iron oxide and iron carbide nanoparticles at 450 1C. The formation of the graphitic carbon phase at such a low temperature is unique and probably obtained by catalysis of the elemental iron nanoparticles. Changing the annealing time period and the ([PVP]/[Fe(CO)5]) ratio allowed control of the composition, size, size distribution, crystallinity, geometrical shape and magnetic properties of the different magnetic nanoparticles

Microwave-assisted ammonia decomposition reaction over iron incorporated mesoporous carbon catalysts

Microwave-assisted ammonia decomposition reaction was investigated to produce COx free hydrogen, for fuel cell applications. Iron incorporated mesoporous carbon catalysts were prepared at different metal loadings, following an impregnation procedure. Mesoporous carbon acted as the catalyst support, as well as the microwave receptor. Complete conversion of ammonia was achieved at 450 degrees C over the catalyst having 7.7 wt% Fe, when the reaction was carried out in the microwave reactor system, using pure ammonia (GHSV of 36000 ml/h gut). However, in the case of using the conventionally heated reactor, complete conversion of ammonia was achieved only at 600 degrees C. Iron oxides, namely maghemite (gamma-Fe2O3), magnetite (Fe3O4) and hematite (alpha-Fe2O3) simultaneously appeared in the structure of the synthesized catalysts, after their calcination at 450 degrees C, under pure N-2 flow. Iron oxides present in the calcined catalytic materials then were reduced to metallic iron at 500 degrees C. Formation of iron carbide crystals was observed in the structure of spent catalysts that were used in microwave reactor system, while metallic iron crystals were still present in the catalysts that were tested in conventionally heated system