| dc.description.abstract | In this master project, bimetallic nanoparticles with nominal composition Pt1-xPdx NPs (0 ≤ x ≤ 1) have been synthesized via a polyol method. PVP was used as the stabilizer/capping agent, Pt(acac)2 and Pd(acac)2 as metal precursors, and 1,4-butanediol as solvent. The precursors were reduced by a simultaneous reduction method. Using these chemicals, the following reaction conditions were established as standard conditions: Reaction temperature of 220°C, aging time of 2 hours, metal/PVP ratio of 1/10, a total amount of 0.2 mmol of metal in 20 mL of solvent. Bimetallic Pt1-xPdx NPs with nominal compositions x = 0; 0.25; 0.50; 0.75; 1 were characterized by powder X-ray diffraction to determine phase purity. It was found that the NPs were phase pure. With respect to the unit cell dimensions, PXRD was not conclusive relative to type of element distribution. NPs with nominal composition Pt0.50Pd0.50 synthesized at standard conditions were studied in more detail with HAADF-STEM-EDX and synchrotron PXRD to determine the elemental distribution in these nanoparticles. It was proved that the elemental distribution was Pd@Pt. Simple visual kinetics experiments, were performed on the Pt(acac)2 and Pd(acac)2 metal precursors to get a better understanding of the core@shell formation. Their relative difference in reaction kinetics for nanoparticle formation was investigated, and it was found that Pd(acac)2 had a much faster reaction kinetics than Pt(acac)2. The nanoparticle formation visually inspected by color change in suspension and documented with STEM-imaging. Through these initial experiments, the conclusion was that the Pd@Pt core@shell elemental distribution is attributed to the large difference in reaction kinetics between the metal precursors. Therefore, a series of experiments were performed in an attempt to tune the relative reaction kinetics between Pt(acac)2 and Pd(acac)2 for nanoparticle formation. In this regard, the reaction kinetics of the precursors were screened in similar but different solvents (ethylene glycol, 1,4-butanediol, 1,2-butanediol, 1,3-propanediol), with two different metal/PVP ratios (1/10 and 1/100). Visual- and STEM-images were used for proving the formation of NPs. It was found that the relative reaction kinetics was not significantly changed by varying these parameters. Another approach was therefore chosen; modifying the standard polyol synthesis by utilizing a successive reduction method. Via this route, we successfully produced Pt seed-NPs with incorporation of Pd. To see if an increased aging time would facilitate diffusion of atomic species in the Pd@Pt nanoparticles synthesized by the standard polyol method, an aging time of 24 hours was selected. Whole Powder Pattern Fitting of synchrotron PXRD results point in the direction of solid solution, however stated with an uncertainty. A general strategy for synthesis of bimetallic nanoparticles with tunable element distribution was developed based on our findings. Main ingredients are to explore the relative kinetics of the metal precursors, choice for successive or simultaneous reduction and to combine PXRD with HAADF-STEM-EDX for the structural analysis. Metal-on-support Pt1-xPdx/Al2O3 (x = 0, 0.10 and 0.50) catalysts have been characterized and evaluated in terms of suitability for NH3 oxidation. The Pt1-xPdx NPs were synthesized by the standard polyol method, and deposited on γ-alumina supports. Nanoparticle size measurements were performed on the basis of BF-TEM images of the free-standing NPs. The composition, and metal loading in the catalyst was determined by ICP-MS, and the catalytic activity was measured by YARA International, Herøya. The TOF for the respective compositions was calculated, and it was found that the pure Pt/Al2O3 catalyst outperformed all other compositions. Further, it was shown that the presence of Pd had a negative effect on the selective oxidation of NH3 to form N2. Moreover, it was established that the characterization technique used for the prepared catalysts needs optimization, in relation to detection of supported noble metal NPs. | eng |