Ir/Al2O3, Ru/Al2O3, and Ir-Ru/Al2O3 catalysts with total metallic contents of 30% in mass were prepared by an incipient wetness method. The characterization of these materials, before and after their use for hydrazine decomposition in a satellite thruster, was performed by measurement techniques of specific surface area, volume and pores size distribution, H-2 chemisorption, TEM and basic chemical analysis. An average decrease of 11% in the BET surface area was observed, independent of the catalyst composition. The total specific pore volume remained unchanged because the volume reduction in the size range diameters between 1.0 and 10 nm was compensated by the increase in the diameters size range between 10 and 100 nm. A reduction of the H-2 quantity adsorbed on the Ir/Al2O3 catalyst can be explained by the metal loss through erosion as well as by its partial occlusion within the pores of the alumina support. On the other hand, catalysts containing Ru showed an increase of H-2 chemisorbed amount, attributed to a more complete reduction of this material after hydrazine decomposition, in spite of the erosion and occlusion losses. Such observations were confirmed by TEM, which showed a great stability of the distributions of the metallic particle sizes in all catalysts. (C) 2003 Elsevier Science B.V. All rights reserved.2502331340