PAMAM Dendrimer-Derived Ir/Al2O3 Catalysts: An EXAFS Characterization

Extended X-ray absorption fine structure (EXAFS) spectroscopy was used to characterize several synthesis stages of hydroxyl-terminated generation four (G4OH) PAMAM dendrimer-derived Ir/gamma-Al2O3 catalyst. The EXAFS results indicate that Ir3+ forms complexes with dendrimer functional groups through displacement of two Cl- ion ligands. These complexes are very stable in solution, and no reduction of Ir3+ to Ir nanoparticles or clusters is observed after introduction of reducing agents such as NaBH4 or H-2. These Ir3+-dendrimer complexes remain essentially intact after support impregnation. The formation of 1-2 nm particles occurs when the catalysts are treated with O-2/H-2 or H-2, and the dendrimer-derived catalysts exhibit a lower degree of metal support interaction.