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Title: Mixed-metal clusters as precursors for bimetallic supported nanoparticle catalysts
Author: Hermans, S.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2001
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This thesis describes in a first part the synthesis of new mixed-metal clusters of ruthenium in association with palladium, platinum and tin. The use of monometallic dichloro complexes of Pd or Pt in reactions with negatively charged penta- or hexaruthenium clusters in the presence of a chlorine scavenger has been moderately successful in the case of Pd, but highly successful in the case of Pt. High yields were obtained in many instances. The mixed clusters [Ru5C(CO)14Pt(COD)], [Ru6C(CO)16Pt(COD)], [Ru6C(CO)15(Pt(COD))2] and [{Ru6C(CO)16}2Pt(MeCN)2] were characterised by X-ray crystallography. On the other hand, the use of [Pt(PPh3)4] allowed the isolation and structure determination of [Ru6C(CO)16PPh3] rather than mixed species. The reactivity of [Ru5C(CO)14Pt(COD)] and [Ru6C(CO)16Pt(COD)] with CO, PPh3 and dppm was investigated, and led to the isolation of other mixed-metal and homometallic compounds. The crystal structures of the clusters [Ru5C(CO)11Pt(CO)(dppm)2], [Ru6C(CO)13(dppm)2] and [Ru6C(CO)16Pt3(dppm)2] were determined. Several Ru-Sn mixed clusters were also synthesised, and in particular reactions involving [PPN]2[Ru6C(CO)16] and SnCl4 led to the isolation of [PPN][Ru6C(CO)16SnCl3] and [Ru6C(CO)16SnCl2], which were characterised crystallographically. In a second part, some of the new mixed-metal clusters were used as precursors for nanoparticle heterogeneous catalysts, using the mesoporous silica MCM-41 or carbon nanotubes as supports. A Ru-Pd/MCM-41 catalyst derived from a Pd6Ru6 cluster was shown to be extremely active for the hydrogenation of alkenes to alkanes and of naphthalene to cis-decalin selectively. This material was characterised by STEM and in situ FTIR and EXAFS, which confirmed the bimetallic nature of the nanoparticles and their homogeneous small sizes and dispersion on the support. The shape of the nanoparticles was further assessed by theoretical calculations. A Ru-Sn/MCM-41 catalyst was prepared from [PPN][Ru6C(CO)16SnCl3] and shown to hydrogenate selectively cyclic poly-enes to their mono-enes, under solvent-free and low temperature conditions. This catalyst was also characterised by STEM and in situ FTIR and EXAFS, which indicated that the tin atom is the anchoring point for the bimetallic nanoparticles on the siliceous walls of MCM-41. Finally, the clusters [Ru5C(CO)14Pt(COD)], [Ru6C(CO)16Pt(COD)], [PPN][Ru6C(CO)16SnCl3] and [Ru6C(CO)16SnCl2] were used as ideal precursors for small-sized and evenly dispersed bimetallic nanoparticles supported on carbon nanotubes.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available