Distribution and Grain Size Support-Dependent Catalytic Properties of Iridium Nanoparticles

Document Type : Original Research Paper


Space Transportation Research Institute, Iranian space research center, Tehran, Iran



The catalytic reaction of iridium nanoparticles was carried out over gamma alumina
granules to investigate the factors controlling the catalytic activities.
The evaluation of iridium nanoparticle activity in the laboratory reactor was
done for support grains with different diameters between 1 mm to 4 mm. The
characterization of three iridium catalysts was evaluated by XRD, FESEM and
EDX before and after catalytic activity. The rate of hydrazine decomposition and
hydrogen selectivity increased to 306 h-1 and 42% with the better distribution
of nanoparticles, regardless of the grain size of catalyst support, whereas the
hydrazine decomposition rate was larger for smaller supported catalysts. The
probability of hydrazine monohydrate molecules in contact with active sites
becomes higher and the movement of reactants and gas products will be easy
inside and outside the pores, leading to the increase in reactivity. The rate of the
hydrazine monohydrate decomposition and H2 selectivity decreased to 216 h-1
and 26% with the lower catalyst grains and the higher size of support along with
worse distribution on the surface. The remarkable results of results prove that
support granule size is a dominant factor in catalytic decomposition.