Studies of the Kinetics of Reaction Between Iron Catalysts and Ammonia-Nitriding of Nanocrystalline Iron with Parallel Catalytic Ammonia Decomposition

Analysis of two parallel chemical reactions was performed using a flow differential tubular reactor with thermogravimetric measurement and analysis of the gas phase composition. The nitriding rate of the iron ammonia synthesis catalyst and the ammonia decomposition rate were investigated at 350-550 A degrees C. Various gas-phase nitriding potentials were applied. Phase composition was analysed by X-ray diffraction. From a comparison with Lehrer diagram, the critical nitriding potentials for nanoiron were found to be higher than that for bulk materials. The rates of nitriding and ammonia decomposition on iron and various nitrides were determined. Ammonia decomposition was the most rapid on alpha-Fe and the slowest on gamma'-Fe(4)N. Results were interpreted on the basis of the adsorption range model and values of kinetics and thermodynamic parameters were assessed. A new method for the determination of crystallite mass distribution, using the results of iron catalyst nitriding process rate measurements, was proposed.