Ammonia decomposition over commercial Ru/Al2O3 catalyst: An experimental evaluation at different operative pressures and temperatures

The ammonia decomposition process for hydrogen production was studied experimentally in a fixed bed tubular micro-reactor (I.D. = 1 cm and h = 20 cm) filled with 15 ml of ACTA Hypermec 10010 Ru catalyst. With the aim of pointing out the best process conditions, experiments were carried out varying the reaction temperature between 400 and 500 C, the feeding gas pressure between 1 and 10 bar and the GHSV (Gas Hourly Space Velocity) between 300 and 2400 h -1. To maintain the temperature as uniform as possible along the reactor axis, a 3 zone heater was used and each zone was controlled independently. An acid H2SO4 trap was used downstream the reactor to remove by neutralization the residual ammonia from the product gas. Moreover, the residual ammonia amount in the gas and thus the NH3 dissociation were evaluated for the catalyst in different operative conditions by measuring the PH of the trap and its changing rate over time. Dissociations close to the chemical equilibrium were obtained for every GHSV and temperature we tested with a pressures of 1 and 5 bar in the reactor. In particular, the dissociation was always higher than 99% at 1 bar, while at 5 bar it varied from 96% at 400 °C to 99% at 500 °C. At 10 bar the chemical equilibrium was reached for all GHSVs only at 450 °C and 500 °C with dissociations equal to 95.5% and 97.2%. At 400 °C a dissociation close to the chemical equilibrium (92%) was reached only for a GHSV of 300 h-1 while for the remaining GHSVs the dissociation was always lower, down to 80.8% for a GHSV equal to 2400 h-1. The kinetic parameters of the Temkin-Pyzhev model were evaluated for the ACTA Hypermec 10010 catalyst starting from the literature data on Ru catalyst. The results of this analysis showed that a pre-exponential factor of 1.5 × 10-9 mol m-3 s-1, an activation energy of 117 kJ mol-1 and a reaction order of 0.27 can be adopted for numerical simulations. Copyright © 2013, Hydrogen Energy Publications, LLC.