Synthesis of Dendrimer-Derived Supported Iridium Catalysts

Catalysts are used extensively throughout our society to synthesize many types of products, including pharmaceuticals and agrochemicals. Some of these reactions utilize iridium as a key component in the catalyst and many of these reactions are structure sensitive. Therefore, controlling the particle size and, thus perhaps, the selectivity of these catalysts is essential for tailoring these materials to specific reactions. In this research, iridium and iridium-palladium based catalysts were synthesized using dendrimer-metal nanocomposites (DMNs) to control the resulting particle size. Fourth-generation hydroxyl-terminated poly(amidoamine) (PAMAM) dendrimers were combined with an aqueous solution of IrCl3 in a 1:40 dendrimer to metal molar ratio. The bimetallic catalysts were synthesized via a co-complexation process, using a molar ratio of 20:20:1 IrCl3 to K2PdCl4 to dendrimer solution. In both cases the complexation process was observed via ultraviolet-visible (UV-vis) spectroscopy. The UV-vis results showed that the complexation reached steady state after seven days for both systems. The complexed systems were then reduced using NaBH4 to form DMNs. The solution was subsequently delivered to an Al2O3 support via standard wet impregnation. The dendrimer was then removed via thermal decomposition to produce nanoparticles on the support. To follow the decomposition of dendrimer, the process was investigated via transmission Fourier transform infrared (FTIR) spectroscopy. The FTIR results show a complete complexation and decomposition of the dendrimer in both catalysts.