Ammonia decomposition over the carbon-based iron catalyst promoted with potassium Original Research Article

Kinetics of NH3 decomposition over the K+-promoted iron catalysts supported on graphitized carbon (surface area=440 m2/g) have been studied under 1 bar pressure. Both the ammonia partial pressure dependence (5–20% NH3 in the H2:N2=3:1 mixture) and temperature dependence of the reaction rates have been determined. The studies demonstrate that the rate of ammonia decomposition (TOF) over K+-Fe/C is influenced by the size of iron particles: smaller particles exhibit higher TOF. The apparent energy of activation for K+-Fe/C (166 kJ/mol) proved to be similar to that for the fused iron catalyst (167 kJ/mol) and significantly higher than the activation energy for K+-Ru/C (139 kJ/mol). The Langmuir–Hinshelwood modeling based on the NH3 decomposition data obtained and corresponding data for NH3 synthesis suggest that the Fe surfaces of the K+-Fe/C catalyst are strongly covered with atomic nitrogen when operating under the high pressure NH3 synthesis conditions.