Structural and catalytic properties of supported Ni-Ir alloy catalysts for H₂ generation via hydrous hydrazine decomposition

Iridium modified Ni/Al₂O₃ catalysts were prepared using Ni-Al hydrotalcite as precursor and tested in the selective decomposition of hydrous hydrazine for H₂ generation. Compared to Ni/Al₂O₃, NiIr_x/Al₂O₃ catalysts exhibited an increase of the reaction rate up to 6-fold and the H₂ selectivity from 93% to above 99%. The XRD and EXAFS analysis confirmed that Ir and Ni were present in the form of Ni-Ir alloy; and the H₂ differential heat of adsorption is appreciably lowered with increasing the amount of Ir in Ni-Ir alloy. High-temperature reduction, e.g. 700°C, induced the migration of Ir atoms into the Ni bulk and produced a Ni-skin surface. This structural modification is associated with a strongly decrease of activity and selectivity. EXAFS measurements were also performed on different noble metals (NM, Ir, Pt, and Au) modified Ni/Al₂O₃ catalysts in order to verify the extent of NM-Ni bimetallic bond formation, which was found to correlate with the catalytic performance.