It is desired that decomposition of ammonia as a promising chemical hydrogen carrier is carried out at lower temperatures, whereby making possible a highly efficient hydrogen recovery from ammonia. Although the equilibrium conversion is almost 100% in the range of 623â??723K, the decomposition remains in a low conversion, so that insufficient activity of present catalysts should be improved. This study attempts to prove that this kinetically limited decomposition using a ruthenium supported catalyst can also be enhanced in the palladium membrane reactor by selective hydrogen separation.
The Langmuir-Hinshelwood types of rate equations, seven reaction models, for ammonia decomposition using a Ru/SiO2 or Ru/Al2O3 catalyst were derived and compared with experimental results. As the result, the combinative desorption of nitrogen atom was found to be the rate determining step in the range of 623â??723 K. One dimensional model for a palladium membrane reactor made clear that the kinetic enhancement differed considerably according to the reaction model (rate expression)
In the ammonia decomposition employing a membrane reactor with a thinner palladium composite membrane tube, a large increase in conversion and hydrogen recovery compared with the conventional packed reactor could be obtained.
