An alumina supported silver catalyst was studied with a transient step-response technique for the reduction of NO and N2O with H-2. Dissociation of hydrogen and deuterium was observed on the Ag/alumina catalyst and a kinetic model was proposed for the isotopic exchange between H-2 and D-2. The proposed model describes the observed dissociation and isotope exchange reaction sufficiently well. (C) 2004 Elsevier B.V. All rights reserved.