Ultra trace analysis and mobility of palladium emissions from automotive catalytic converters

Abstract

Palladium (Pd) is emitted as particles and nanoparticles in considerable amounts from automotive catalytic converters along with the exhaust fume. In the environment Pd nanoparticles may be coated by small organic molecules or dissolve to Pd(II) species. Transformation and mobility of Pd in nature is not well understood yet and have to be investigated due to possible environmental and health risks. In the first part of this thesis a method for the determination of Pd in urban samples, such as roadside soil and road dust, is described. The developed method comprises total matrix decomposition by microwave-assisted pressurized digestion. Subsequent preconcentration of Pd(II) is based on an automated flow injection system, which includes a ligand-assisted solid-phase microextraction with (N, N)-diethyl-(N’)-benzoylthiourea. Pd(II) is selectively complexed by the ligand and thereby both separated from the matrix and enriched. Pd(II) in the resulting elution was quantitatively determined by high-resolution graphite furnace atomic absorption spectrometry. In the second part of this thesis the mobility of different Pd nanoparticle species and Pd(II) salts in water-saturated porous media is presented. Here, the coated Pd nanoparticles had a higher mobility compared to the non-coated Pd nanoparticles and the Pd(II), which were almost completely retained by silica, sand, and potting soil. In a collaborative project the influence of the small complexing agents ethylenediaminetetraacetic acid and L-methionine on the solubility of Pd(0) was investigated. Here, initial reaction rates were determined and compared to literature values. Finally, the synthesis and characterization of model nanoparticle aqueous suspensions, i.e. three different colloidal Pd nanoparticle solutions and one colloidal platinum nanoparticle solution, is described. These suspensions served as surrogate in different mobility and toxicological experiments to model Pd and Pt emissions into the environment.