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Faculty of Biology, Chemistry & Earth Sciences

Solid state chemistry – mesostructured materials: Juniorprofessor Dr. Mirijam Zobel

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Noble metal NPs in catalysis

Correlation of solvent restructuring with the catalytic activity of noble metal nanoparticle

Heterogeneous catalysts are used in more than 90 % of modern industrial syntheses of chemicals and pharmaceuticals. Supported noble metal nanoparticles obtain much attention because they combine the advantages of heterogeneous and homogeneous catalysts. [1] The activity and selectivity of those catalysts is influenced on the one hand by their size and shape [2], and on the other hand by reaction parameters such as solvent, temperature and pressure. [3] Although the solvent effect is known to play a major role and contributing parameters such as the solvent polarity have been identified in the past, there is not yet a fundamental understanding of the solvent interface at the nanoparticle surface during liquid-phase heterogeneous catalysis. As physico-chemical properties are derived from atomistic and molecular structures, we want to gain insight into the solvent structure at the interface to correlate it with the catalytic behaviour. Just recently by means of pair distribution function (PDF) analysis, we showed that 3 to 5 layers of solvent molecules reorient at the NP-solvent interface. The solvent molecules feature a local structure different from the bulk. [4]

Within this PhD project gold nanoparticles of different diameters from 3 to 10 nm are synthesized with three different kinds of stabilizers, e.g. polymers, tensides and organic molecules. They are characterized by dynamic light scattering, UV-Vis spectroscopy, thermogravimetic analysis, tunneling electron microscopy and X-ray diffraction analysis. These gold nanoparticles are used as catalyst in the hydrogenation of 4-nitrophenol to 4-aminophenol with the reducing agent sodium borohydride as model reaction. This catalysis proceeds in water under mild conditions at room temperature and atmospheric pressure and can be analyzed by spectroscopic methods. [5]

[1] D. Atruc et al., Angew. Chem. Int. Ed. 2005, 44, 7852.

[2] K. An et al., ChemCatChem 2012, 4, 1512.

[3] U. K. Singh et al., Appl. Catal., A 2001, 213, 1.

[4] M. Zobel et al., Science 2015, 347.

[5] P. Herves et al., Chem. Soc. Rev. 2012, 41, 5577.

Associated PhD candidate: MSc Mirco Eckardt


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