- 4:42 PM

Synthesis and Characterization of Dendrimer-Derived Ir/Γ-Al2O3 Catalysts

Yaritza M. López-De Jesús, Oleg S. Alexeev, and Christopher Williams. Chemical Engineering Department, University of South Carolina, Swearingen Engineering Center 2C02, 301 S Main St., Columbia, SC 29208

We report the synthesis of 1wt% Ir/g-Al2O3 catalyst using a dendrimer-metal nanocomposite (DMN) precursor to control the resulting Ir particle size.  Fourth generation hydroxyl-terminated polyamidoamine (PAMAM-OH) dendrimer was combined with IrCl3 in aqueous solution at room temperature in a metal-dendrimer molar ratio of 40:1.  The complexation process between Ir and the dendrimer amine and amide groups was followed using ultraviolet-visible (UV-Vis) spectroscopy.  The results suggest that seven days are required to reach equilibrium, after which the DMN solution saturated with H2.  The resulting DMN precursor is delivered to a g-Al2O3 support via standard wet impregnation.  The dendrimer is subsequently removed by thermal decomposition in order to produce nanoparticles on the support. This process was investigated using transmission Fourier transform infrared (FTIR) spectroscopy to follow the decomposition of dendrimer into various fragments and their subsequent desorption from the surface.  In addition, FTIR measurements during CO adsorption were performed to identify the catalyst activation treatment that exposed the greatest number of metal sites. Two different optimal treatments were found:  350°C in O2 for 30 min/400°C in H2 for 1 hr treatment or H2 at 400°C for 2 hrs.  In addition, this catalyst has been characterized using high resolution transmission electron microscopy (HRTEM) to obtain particle size distributions and extended X-ray absorption fine structure (EXAFS) spectroscopy develop a better understanding of the dendrimer-Ir molecular interactions.  These results will be compared with similar measurements from traditionally prepared Ir catalysts.  The effectiveness of this novel approach for control of metal particle size/dispersion will be discussed in light of these findings.