Kinetic studies on ammonia decomposition over zirconium oxynitride

The kinetics of ammonia decomposition has been studied using a zirconium oxynitride catalyst, which has been synthesized via ammonolysis of zirconia. The catalyst was characterized with BET, XRD and hot gas extraction. The conversion of NH3 was measured as a function of residence time, temperature, partial pressures of H2 and NH3 in the inlet flow, respectively, via infrared spectrometry. The activation energy of the rate determining step and adsorption enthalpies were determined for a 3 and a 5-step reaction mechanism, considering an interaction between NH3 and the oxygen vacancies of the catalyst. A comparison with theoretically predicted values offered a good agreement and led to a refinement of the mechanism.Research highlights▶ Reaction mechanism for decomposition of ammonia over zirconium oxynitride. ▶ Determining of equilibrium constants and activation energy. ▶ Link between theoretical works and experiment.