Temperature-programmed surface reaction (TPSR) experiments with a ruthenium-based catalyst supported on MgO were conducted in a microreactor flow system. The hydrogenation of preadsorbed atomic nitrogen obtained under various experimental conditions has been studied followed by a detailed microkinetic analysis including an evaluation of the influence of backmixing, The shape of the TPSR profile was found to depend strongly on the initial surface coverage and on the presence of coadsorbates.