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Nanoscopic Transition Metals Colloidal Precursors, Networks, And Catalysts

Posted on:2005-03-20Degree:DoctorType:Dissertation
Country:ChinaCandidate:F WenFull Text:PDF
GTID:1101360152475583Subject:Applied Chemistry
Abstract/Summary:PDF Full Text Request
Previous work has shown that aluminium trialkyls can be used successfully to prepare colloidal mono- and bimetallic nanoparticles by "reductive stabilization". Two major advantages of this methodology are that: (1) no surfactant is required for the preparation of nearly monodisperse transition metal colloids, and (2) these nanoparticles have highly reactive organo-Al groups as colloidal stabilizers, which can then be chemically modified to tailor their dispersion characteristics and even to develop 2-D or 3-D nanoparticle networks.The present work extends the "reductive stabilization" to low-valeht organometallics with the aim of obtaining monodisperse transition metal colloids (Pt, Ni, Pt-Ru) having reactive protective shells. The size-selective syntheses of these transition metal colloids were explored.By analogy with the aluminium organic route, organoborane compounds were applied to the preparation of Ni colloids stabilized by B-organic shells.The reactive organo-Al or organo-B groups in the stabilizers of Pt and Ni colloids allow nanoparticle networks to be formed via protonolytic action of bifunctional "spacers". Control of the inter-particle distance can be achieved by using spacer molecules with different lengths.Based on the "precursor concept", Pt and Pt-Ru colloid precursors stabilized by Al-organyls were used to prepare fuel cell catalysts on Vulcan XC-72. The electrochemical activity in the oxidation of CO or methanol was investigated by the thin-film rotating disk electrode (RDE) method. In particular, leaching effect, i.e., the removal of Al protective shells, was discovered.With respect to homogeneous catalysis, the thermoregulated Rh complex catalyst was shown to form colloidal Rh after the repeated catalytic cycles. Ultimately, as a result of Ostwald ripening, the colloids grow and form metal precipitates, causing them to lose their activity.
Keywords/Search Tags:Transition metal colloids, Reductive stabilization, Nanonetworks, Electrochemistry catalysts, Thermoregulated phase-transfer catalysis
PDF Full Text Request
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