Metal nanoclusters exhibit unique properties which differ from their bulk
materials, owing to the quantum size effects. For example, the catalytic activity of
transition metal nanoclusters generally increases with decreasing particle size.
However, nanoclusters tend to be fairly unstable with respect to the agglomerate into
bulk metal in solution and thus special precautions have to be taken to avoid their
aggregation or precipitation during the preparation of such nanoclusters in solution.
In order to obtain stable nanoclusters dispersed in solution, a stabilizing agent is
usually added into the reaction system. The stabilization of metal nanoclusters in
solution can be achieved either by electrostatically by using charged ions such as
acetate ion or sterically by long chain molecules such as polymers. Polymers are one
of the most widely used steric stabilizers for the preparation of stable metal
nanoclusters in solution. The use of polymers as stabilizer for the synthesis of
transition metal nanoclusters provides advantegous regarding solubility,
conductivity, thermal stability and reusability. The metal nanoclusters stabilized by
polymers generally show higher catalytic activity, stability and optical properties. In
this dissertation we report the preparation and characterization of water soluble
polymer stabilized transition metal(0) (metal= Ni, Co and Ru) nanoclusters and their
v
catalysis in hydrogen generation from the hydrolysis of sodium borohydride
(NaBH4) and ammonia borane (AB) which are the best candidates as chemical
hydrogen storage materials for on-board applications. The water soluble polymer
stabilized nickel(0), cobalt(0) and ruthenium(0) nanoclusters were prepared by using
two different facile methods / (i) the reduction of metal precursors by sodium
borohydride in the presence poly(N-vinyl pyrrolidone) (PVP) in methanol solution
after 1h reflux, (ii) the in situ generation during the hydrolysis of ammonia borane in
the presence of poly(4-styrene sulfonicacid-co-maleic acid) (PSSA-co-MA). The
characterization of both type of polymer stabilized transition metal(0) nanoclusters
were done by using UV-Visible electronic absorption spectroscopy (UV-Vis),
transmission electron microscopy (TEM), high resolution transmission electron
microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction
(XRD) and FT-IR techniques. The catalytic activity of PVP stabilized nickel(0),
cobalt(0) and ruthenium(0) nanoclusters was tested in the hydrolysis of NaBH4 and
AB. The catalytic acitivity of PSSA-co-MA stabilized nickel(0), cobalt(0) and
ruthenium(0) nanoclusters was tested only in the hydrolysis of AB in which they
were in situ generated. The kinetics of hydrogen generation from both hydrolysis
reactions in the presence PVP or PSSA-co-MA stabilized nickel(0), cobalt(0) and
ruthenium(0) nanoclusters were studied depending on the polymer to metal ratio,
catalyst concentration, substrate concentration and temperature as well as the
activation parameters (Arrhenius activation energy (Ea), activation enthalpy (
| Identifer | oai:union.ndltd.org:METU/oai:etd.lib.metu.edu.tr:http://etd.lib.metu.edu.tr/upload/12612717/index.pdf |
| Date | 01 December 2010 |
| Creators | Metin, Onder |
| Contributors | Ozkar, Saim |
| Publisher | METU |
| Source Sets | Middle East Technical Univ. |
| Language | English |
| Detected Language | English |
| Type | Ph.D. Thesis |
| Format | text/pdf |
| Rights | To liberate the content for public access |
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