SYNTHESIS, CHARACTERIZATION AND ACTIVITY OF IRON OXIDE NANOCATALYST FOR AMMONIA PRODUCTION

Ammonia synthesis was evaluated in the presence of α-Fe2O3, Fe3O4 and 5% α-Fe2O3/γ-Al2O3 nanocatalysts. The nanocatalysts were prepared via sol-gel and sol gel-hydrothermal methods. The variables studied for synthesis using sol gel method were stirring period and annealing temperature. Samples were characterized using x-ray diffraction (XRD), raman spectroscopy, field emission scanning electron microscopy (FESEM), energy dispersed x-ray (EDX), temperature programmed reduction (TPR), vibration sample magnetometer (VSM) and N2 adsorption. Extending synthesis period from 1 day to 1 month in the sol gel method reduced the size of α-Fe2O3 nanocatalyst particles from 60 nm to 27 nm. Particle size increased from 21 nm to 60 nm when the annealing temperature was increased from 300oC to 700oC. The sol gel-hydrothermal produced a well crystallined Fe3O4 nanocatalyst at synthesis temperature of 160oC. The 5% α-Fe2O3/γ-Al2O3 prepared using sol gel-hydrothermal method at iron nitrate to sodium bis(2-ethylhexyl) sulfucinnate surfactant ratio of 2:3 exhibited better particles dispersion compared to those prepared at other ratios. The TPR profiles for the nanocatalysts exhibited two reduction stages for the transformations of α-Fe2O3 to Fe3O4 and Fe3O4 to α-Fe. For the unsupported α-Fe2O3, reduction peaks were observed at 400oC to 460oC and 680oC to 780oC regions whereas for the γ-Al2O3-supported α-Fe2O3, the reduction peaks shifted to 350oC to 400oC and 550oC to 650oC. The catalytic study was conducted in a fixed bed microreactor at 30oC to 200oC under atmospheric pressure with a total feed flow rate of 40 cm3/min and H2/N2 volume ratio of 3:1. The amount of ammonia was determined using an acid-base titration method. The ammonia yield over α-Fe2O3 and 5% α-Fe2O3/γ-Al2O3 catalysts at 110oC measured in the absence of magnetic field was 2.65 %/gFe and 26.3 %/gFe, respectively. Applying magnetic field at 1 Tesla to the α-Fe2O3 catalyst resulted in two orders of magnitude increase in the ammonia yield while using Fe3O4 nanocatalyst further enhanced the ammonia yield by about 14% greater than that of α-Fe2O3. The performance of nanocatalysts for the ammonia synthesis in the absence and presence of magnetic field can be ranked as 5% α-Fe2O3/γ-Al2O3> α-Fe2O3 and Fe3O4> α-Fe2O3, respectively