Synthesis and characterization of free standing Pt-Rh nanoparticles, and 2 wt. % Pt0.70Rh0.30/Al2O3 and 20 wt. % Co1xRex/Al2O3 (0.00 ≤ x ≤ 0.15) metal-on-support catalysts

Abstract

In this project three different chemical systems are investigated with respect to synthesis and characterization; Pt1xRhx (0.00 ≤ x ≤ 1.00) nanoparticles (~5-17 nm), 2 wt. % Pt0.70Rh0.30/Al2O3 catalysts for ammonia oxidation and 20 wt. % Co1xRex/Al2O3 (0.00 ≤ x ≤ 0.15) catalysts for Fischer-Tropsch catalysis. An apparatus for synthesis of monodisperse metallic nanoparticles by the polyol route is constructed, and the synthesis route is established. Pt1xRhx nanoparticles have been produced. The effect of reaction time (0.5 – 3 h) and reaction temperature (190 – 230 oC) on particle size and particle size distribution are studied, keeping other essential parameters constant (metal salt precursor(s): surfactant ratio, dilution, type of solvent and surfactant). All samples have been characterized by PXD to inspect sample purity, to extract unit cell dimensions as well as to estimate particle size. Evaluations of the variation in unit cell dimensions (a-axis) with degree of Rh substitution (x) indicate that the particles form a complete solid solution. High resolution SEM is used to map the particle size distribution (typically analyzing 200 particles per sample) and to study particle morphology. For some few selected samples DLS is used to evaluate the freshly synthesized particles in suspension. Four different 2 wt. % Pt0.70Rh0.30/Al2O3 catalysts are produced. The catalysts are produced by depositing free standing Pt0.70Rh0.30 particles onto two different supports. The nanoparticles are synthesized using two different approaches to synthesise nanoparticles the round-flask and microwave method. Both methods are based on that metal nanoparticles are produced by reducing the corresponding metal salt precursors. Morphology of the nanoparticles from the synthesis step to the ready catalysts are evaluated together will how well the particles are dispersed on the Al2O3 support. TEM, 1. BET, ICP-MS and PXD have been used in the characterisation work. The catalysts will at a later stage be externally evaluated for ammonia oxidation. By means of incipient wetness impregnation some 20 wt. % Co1xRex/Al2O3 (0.00 ≤ x ≤ 0.15) catalysts are prepared. The samples were calcinated and reduced after the impregnation step. PXD is used investigate phase content of the samples after both the calcination- and reduction step. The materials will be used in an up-coming SXRD experiment at ESRF in Grenoble, France.