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Lai, Yungchieh (2013) BIMETALLIC GOLD AND PLATINUM NANOCATALYSTS IN WGS. Master's Thesis, University of Pittsburgh. (Unpublished)

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The water gas shift (WGS) reaction plays an important role for hydrogen production from fossil and renewable resources. As an exothermal reaction, it is limited by thermodynamic equilibrium at high temperature and by slow kinetics at low temperatures. In order to achieve a high-equilibrium conversion and overcome slow kinetics, multifunctional catalysts for WGS have been widely studied. Au-based catalysts in particular have recently emerged as promising for low-temperature WGS, but the limited stability of Au is a major concern for technical application of these catalysts.
Cao and Veser recently demonstrated that alloying of metal particles can result in highly active nanocatalysts with exceptional high-temperature stability. In those studies, metals with essentially complete miscibility across the entire range of compositions were utilized. In the present study, we evaluated the extension of this principle onto catalysts with a wide miscibility gap by alloying Au nanoparticles with Pt. Both metals are known to show good WGS activity, but Pt has a much higher melting point and hence better thermal stability than Au.
AuPt bimetallic nanoparticles (NPs) were prepared by co-reducing polyvinylpyrrolidone (PVP) protected Au and Pt precursors with sodium borohydride in aqueous solution. Despite the wide miscibility gap between the two (bulk) metals, we were able to form well-controlled, homogeneous bimetallic NPs over a broad range. The as-synthesized NPs were then deposited onto ceria and silica as supports. The materials were characterized using a range of techniques,
Yungchieh Lai, M.S.
University of Pittsburgh, 2012
including XRD, TEM, HRTEM, and UV-Vis, and then evaluated with regard to thermal stability during calcination in air. We found that the bimetallic nanoparticles spread on the two supports exhibit different phase behaviors during heat treatments, albeit they all suffer partial or complete phase segregations. While AuPt/SiO2 phase-separates into the thermodynamically stable Au-rich and Pt-rich phases already at T>400°C and become a Pt-core/Au-shell structure, the bimetallic nanoparticles deposited on ceria undergoes a complete phase segregation into separate Au and Pt-rich nanoparticles during heat treatments, and only fused to form the thermodynamically stable phases at T ~900°C. Clearly, metal-support interactions strongly dominate the behavior of this bimetallic system. Fixed-bed reactor and the TPD experiments further demonstrate that the WGS activity of these catalysts strongly correlate with the phase stability of the bimetallic nanoparticles. Overall, our results demonstrate that, while previously suggested principle of catalyst stabilization via alloying with a higher melting-point component may hold even for systems with a miscibility gap, metal-support interactions are critical in the consideration of materials stability and can even dictate catalyst stability.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Lai, Yungchiehyul69@pitt.eduYUL69
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairVeser, Götzgveser@pitt.eduGVESER
Committee MemberLi, Leilel55@pitt.eduLEL55
Committee MemberJin,
Date: 31 January 2013
Date Type: Publication
Defense Date: 7 November 2012
Approval Date: 31 January 2013
Submission Date: 9 November 2012
Access Restriction: 5 year -- Restrict access to University of Pittsburgh for a period of 5 years.
Number of Pages: 62
Institution: University of Pittsburgh
Schools and Programs: Swanson School of Engineering > Chemical Engineering
Degree: MS - Master of Science
Thesis Type: Master's Thesis
Refereed: Yes
Uncontrolled Keywords: Bimetallic catalysts, Water-gas shift
Date Deposited: 31 Jan 2013 20:13
Last Modified: 31 Jan 2018 06:15


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