Development of allotropic noble metal nanoparticles for improved catalysis

Promovendus/a: Michaël Gebruers

Promotor(en): Prof. dr. ir. Maarten Roeffaers

Noble metal nanoparticles (NPs) are often used as a catalyst due to their unique properties, such as their increased surface-to-volume-ratio, compared to their bulk counterparts. The influence of NP size and shape on the catalytic activity of noble metal NPs has been widely explored, the influence of the crystal phase has however gained much less attention. In recent years, allotropic NPs of various metals have successfully been obtained, their synthesis and catalytic applications have however not been fully explored. This Ph.D thesis aims to broaden the current knowledge on the synthesis, characterization and catalytic applications of noble metal NPs. This is achieved by studying allotropic silver and ruthenium NPs. Various allotropic structures of silver NPs have been reported, but their synthesis over regular silver NPs has not been investigated in detail. This often leads to the formation of silver NPs with multiple crystal structures. In the first part of this thesis the synthesis of allotropic hexagonal close-packed (hcp) silver NPs, over regular face-centered cubic (fcc) silver NPs, was optimized. Furthermore, the characterization of hcp silver NPs via XRD was optimized to yield an unambiguous method to distinguish them from regular fcc silver NPs. In the second part of this thesis, the catalytic activity of allotropic ruthenium NPs was studied as a photo- and thermal catalyst. It was demonstrated that both regular hcp and allotropic fcc ruthenium NPs perform very differently depending on the reaction at hand. It could be concluded that different allotropic structures of a material perform differently in different catalytic applications, indicating that there is not one better catalyst when comparing metal allotropes, but that the best performing allotrope will strongly depend on the catalytic reaction at hand.