Logo for the University of Illinois at Chicago
    • Login
    View Item 
    •   INDIGO Home
    • Dissertations and Theses at UIC
    • UIC Dissertations and Theses
    • View Item
    •   INDIGO Home
    • Dissertations and Theses at UIC
    • UIC Dissertations and Theses
    • View Item
    JavaScript is disabled for your browser. Some features of this site may not work without it.

    Effect of Pretreatment on Metal Dispersion in Carbon and Oxide Supported Catalysts

    Thumbnail
    View/Open
    Nieto_Manuel.pdf (8.630Mb)
    Date
    2012-12-13
    Author
    Nieto, Manuel A.
    Metadata
    Show full item record
    Abstract
    One of the most important concerns in catalyst synthesis is metal particle size. In heterogeneous catalysis, chemical reactions of the gas phase occur with the metal atoms at the surface of the particles. A high level of dispersion is critical to maximize the amount of surface metal atoms. After impregnation of the support with the metal precursor, the pretreatment conditions of the catalyst play a crucial role in determining the final metal particle size. This correlation has been indirectly investigated by various studies, but hasn’t been systematically examined. This research deals with the influence that temperature and heating rate, during reduction in hydrogen gas, have on platinum and palladium particle size on various supports, both low PZC (oxidized carbon, TiO2, SiO2) and high PZC (carbon, Al2O3). The influence of humidity during reduction is also studied for the Pt catalysts. The shape of the particle size distribution offers valuable information to determine if a particular sintering mechanism, Ostwald Ripening (OR) or Particle Migration and Coalescence (PMC), has taken place. For this study, the catalysts are synthesized by dry impregnation (DI) and strong electrostatic adsorption (SEA). Particle size analyses were done by XRD and STEM imaging. Even though particle sizes widely vary between supports, the metal used, and the preparation method, general results show a range from 0.9 to 15 nm, where lower heating rates and lower reduction temperatures favor the formation of smaller particles. The presence of humidity during reduction was found to cause extensive sintering. The particle size distributions obtained from STEM imaging reveal PMC is the predominant sintering mechanism at work although further evidence suggests OR could be happening as well for some systems.
    Subject
    catalyst preparation
    catalyst pretreatment
    sintering
    dispersion
    platinum
    palladium
    reduction
    metal particle size
    Type
    thesis
    text
    Date available in INDIGO
    2012-12-13T21:33:56Z
    URI
    http://hdl.handle.net/10027/9487
    Collections
    • UIC Dissertations and Theses

    DSpace software copyright © 2002-2015  DuraSpace
    Contact Us | Send Feedback | Privacy Statement
    Theme by 
    Atmire NV

    Browse

    All of INDIGOCommunities & CollectionsBy Issue DateAuthorsTitlesSubjectsThis CollectionBy Issue DateAuthorsTitlesSubjects

    My Account

    LoginRegister

    Statistics

    View Usage Statistics

    DSpace software copyright © 2002-2015  DuraSpace
    Contact Us | Send Feedback | Privacy Statement
    Theme by 
    Atmire NV