Modelling of tubular ammonia decomposition reactors for fuel cell applications

There is an increasing interest in the use of ammonia as hydrogen carrier for fuel cell applications. Ammonia decomposes catalytically into hydrogen and nitrogen without the emission of catalyst poisoning or polluting gases such as CO. Ammonia decomposition in a catalytic wall reactor is modelled and calibrated using actual experimental data in order to compare the derived model parameters such as activation energy, pre-exponential factor and turn over frequency with data from literature. Turn over frequencies in the range from 24molecules.NH3.Site(-1)s(-1) to 0.31molecules. NH3.site(-1)s(-1), depending on temperature, initial concentration and flow rate applied were calculated from the fitted parameters, which compare well with literature values in the range of 4.21s(-1) to 0.55molecules.NH3.site(-1).s(-1) for Ni catalysts. Similarly activation energies of 165kJ.mol(-1) compare well with data for Ni films (180W.mol(-1)) and Ni wires (209kJ.mol(-1)). A number of conclusions are also drawn from the modelling results suggesting that simplifications to the flow and concentrations profiles may be made.