The catalytic reaction of iridium nanoparticles was carried out over gamma aluminagranules to investigate the factors controlling the catalytic activities.The evaluation of iridium nanoparticle activity in the laboratory reactor wasdone for support grains with different diameters between 1 mm to 4 mm. Thecharacterization of three iridium catalysts was evaluated by XRD, FESEM andEDX before and after catalytic activity. The rate of hydrazine decomposition andhydrogen selectivity increased to 306 h-1 and 42% with the better distributionof nanoparticles, regardless of the grain size of catalyst support, whereas thehydrazine decomposition rate was larger for smaller supported catalysts. Theprobability of hydrazine monohydrate molecules in contact with active sitesbecomes higher and the movement of reactants and gas products will be easyinside and outside the pores, leading to the increase in reactivity. The rate of thehydrazine monohydrate decomposition and H2 selectivity decreased to 216 h-1and 26% with the lower catalyst grains and the higher size of support along withworse distribution on the surface. The remarkable results of results prove thatsupport granule size is a dominant factor in catalytic decomposition. پرونده مقاله