The reaction of ammonia decomposition and nitriding reaction as an example of the parallel reactions were studied. A surface reaction was assumed as the rate limiting step. The experiments were carried out in the range of temperatures from 623 to 723 K. Mixtures of different iron nitrides (gamma'-Fe(4)N, epsilon-Fe(3-2)N) were obtained. Differential tubular reactor with thermogravimetric (TG) measurement and analysis of the gas phase composition in the reaction volume was used. Reacting gases flowing through the reactor were mixed. Effective reactor volume was determined. The rate constants for ammonia decomposition and ammonia adsorption process at critical point between alpha-Fe and gamma'-Fe(4)N phases were estimated. The number of collisions and the sticking coefficient of ammonia over alpha-Fe phase were also assessed.

The catalytic ammonia decomposition over iron and iron nitride, Fe 4 N, under the atmosphere of ammonia-hydrogen mixtures of different amounts of ammonia in the temperature range of 400-550°C by means of thermogravimetry has been studied. A differential tubular reactor with mixing has been used. The ammonia concentration in the gas phase during all the process was analysed. The balance between the inlet and outlet ammonia quantity has been used to determine a degree of ammonia conversion and the values of decomposition reaction rate. The activation energy of ammonia decomposition reaction over Fe and Fe 4 N was found to be 68 and 143 kJ/mol, respectively.

Activity of cobalt and iron catalysts in ammonia synthesis was determined under a pressure of 10 MPa and at the temperature range of 673-823 K, in a sixchannel integral steel reactor. The catalytic ammonia decomposition was studied in a differential reactor under the atmosphere of low concentration of ammonia (\6%) in the temperature range of 673-823 K under atmospheric pressure. The determined values of the activation energy for the ammonia synthesis reaction over cobalt and iron catalysts are 268 and 180 kJ/mol, respectively, whilst for the ammonia decomposition reaction they are equal to 111 and 138 kJ/mol. The cobalt catalyst showed lower activity than a commercial iron catalyst in ammonia synthesis reaction. The cobalt catalyst turned out to be more effective in ammonia decomposition reaction than the iron one.

Promoted nanocrystalline iron was nitrided in a differential reactor equipped with systems that made it possible to conduct both thermogravimetric measurements and hydrogen concentration analyses in the reacting gas mixture. The nitriding process, particularly catalytic ammonia decomposition reaction, was investigated under an atmosphere of ammonia-hydrogen mixtures, under atmospheric pressure. Ammonia concentrations, and so nitriding potentials, were changed gradually from 0 to 100% at the inlet of reactor. The temperature was changed in the range of 475-500 degrees C. While values of nitriding potential were increasing, the rate of catalytic ammonia decomposition on alpha-Fe(N) was increasing too, but on mixture of alpha-Fe(N) with gamma'-Fe(4)N nitride the rate was decreasing. The obtained results were interpreted on the basis of the adsorption range model. New equations describing the catalytic ammonia decomposition reaction rate as a function of the logarithm of the nitriding potential of the gas phase, temperature, and nitriding degree of solid samples were proposed.

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°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 a-Fe and the slowest on c 0 -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.