Thesis (M.Sc.)--York University, 2004. Graduate Programme in Chemistry. / Typescript. Includes bibliographical references (leaves 117-120). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL:http://gateway.proquest.com/openurl?url%5Fver=Z39.88-2004&res%5Fdat=xri:pqdiss&rft%5Fval%5Ffmt=info:ofi/fmt:kev:mtx:dissertation&rft%5Fdat=xri:pqdiss:MQ99407

This thesis discusses the effect of initial particle size and alloying of Pt nanocatalysts on the degradation of Proton Exchange Membrane Fuel Cells (PEMFC). Platinum nanocatalysts with initial particle sizes of 2.2nm, 3.2nm, 5.0nm, 6.7nm and 11.3nm were studied, before and after potential cycling. The two smallest initial particle sizes show significant degradation, while the remainder of the samples show negligible degradation after 10,000 cycles. Among the possible degradation mechanisms operating, the results show that dissolution and re-precipitation is insignificant among all the samples. On the other hand, modified electrochemical Ostwald ripening (MEOR) is the main cause for particle growth and degradation of the Pt nanocatalysts. Moreover, MEOR could also assist the coalescence of particles. Thus, controlling the Pt dissolution rate is the key factor to prevent degradation. In the case of Pt₃Co nanocatalysts, both MEOR as well as dissolution & reprecipitation play an irrelevant role in degradation. However, particle migration and coalescence seems to be more severe in Pt₃Co nanoparticles than for Pt nanoparticles. / text

No description available.

No description available.

No description available.

The heterogeneous metallocene catalyst is becoming a very competitive industrially due to its ability to produce tailor-made polymers. The main advantage of the metallocene polymer product is the narrow molecular weight distribution (MWD) and the systematic comonomer distribution along the polymer chains. Therefore, the metallocene polymer product has well-defined mechanical and optical properties. The aim of this thesis is to investigate the effects of the silica support on the reaction kinetics and micro properties of the heterogeneous metallocene catalyst system. These investigations include studying the influence of the pore volume, surface area, particle size distribution, and the surface chemical characteristics of silica support on the catalyst performance. The experiments showed that the silica type has an influence on the kinetic behavior. For instance, silica with a lower pore volume shows an induction period when compared with higher pore volume silicas. Moreover, the silica type has a clear influence on catalyst activity and polymer morphology. The smallest silica particles produced the highest activity among the other sizes regardless of silica type. The supported catalysts were characterized and linked to the silica type and size in terms of catalyst activity and polymer morphology. Each catalyst in terms of silica type behaved similarly regardless of type of alkylaluminum used in the formulation. The micro properties of the produced polymers, such as MWD and chemical composition distribution (CCD), were studied to understand the effects of the type and size of silica support and co-catalyst on these properties. The silica types showed no effect on the MWD, but had a slight effect on the CCD. Silica with a high pore volume had a stronger more comonomer response. However, the silica particle size had an influence on the CCD, with less comonomer incorporation observed with smaller silica particles. Finally, triethylauminum was observed to produce polymer with a different MWD when compared with other alkylaluminums. However, all alkylaluminums used in this work had no effect on the CCD of the produced polymer regardless of silica type. / Thesis (Master, Chemical Engineering) -- Queen's University, 2012-04-11 13:37:09.878

No description available.

Thesis (Ph.D.) -- McMaster University, 1998. / Includes bibliographical references. Also available via World Wide Web.

Thesis (M.S.)--West Virginia University, 1999. / Title from document title page. Document formatted into pages; contains x, 98 p. : ill. (some col.) Includes abstract. Includes bibliographical references (p. 63-68).

Thesis (M.S.)--University of Wyoming, 2009. / Title from PDF title page (viewed on May 20, 2010). Includes bibliographical references.