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Cobalt-support compound formation in alumina-supported cobalt catalysts

Jongsomjit, Bunjerd (2002) Cobalt-support compound formation in alumina-supported cobalt catalysts. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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Supported cobalt (Co) catalysts are the preferred catalysts for Fischer-Tropsch synthesis (FTS) based on natural gas. However, Co-support compound formation (Co-SCF) can result in lower activity. It has been found that water vapor present during standard reduction affects the degree of reducibility.The impact of water vapor on Co-SCF and the resulting characteristics of Co/g-Al2O3 and CoRu/ g-Al2O3 catalysts were investigated to develop a better understanding of Co-SCF and the effect of Ru promotion on this formation. The degree of reduction was lower when additional water vapor was introduced during reduction, but to a lesser degree when the Ru promoter was present. It is suggested that the Co "aluminate" formed is not identical to CoAl2O4 (spinel) but is probably a surface compound deficient in Co. This Co-SCF is a major cause for differences seen in the degree of reducibility, H2 chemisorption capacity, and Fischer-Tropsch synthesis (FTS) activity. To minimize Co-SCF, the effect of reduction gas containing carbon monoxide (CO) was investigated. A H2 flow containing CO (1-9 vol%) was used for standard reduction. After reduction, the pretreated catalyst samples were characterized and CO hydrogenation also performed. Both initial and steady-state rates went through a maximum for the addition of 3-5 vol% CO during standard reduction. It is concluded that the addition of CO during reduction has a significant effect on activity of the catalyst due to increases in both Co reducibility and dispersion. The effect of metal promoters, such as Cu and Zr on Co-SCF was also investigated. However, Cu addition was found to decrease FTS rate.The impact of Zr modification of alumina had a significant impact on the catalyst properties: FTS rate per gram catalyst increased by a factor of two and reducibility also increased. The impact of Zr modification is likely due to stabilization of the alumina support, prevention or blockage of Co surface "aluminate" formation, and an increase in Co reducibility. Steady-state isotopic transient kinetic analysis (SSITKA) results for CO hydrogenation showed an increase in number of active surface intermediates (NM) while the intrinsic activity (1/tM) remained constant.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Jongsomjit, Bunjerdbujst@pitt.eduBUJST
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairGoodwin, James
Committee MemberWender,
Committee MemberRajgopal,
Committee MemberMcCarthy, Joseph
Committee MemberChiang,
Date: 14 May 2002
Date Type: Completion
Defense Date: 10 May 2002
Approval Date: 14 May 2002
Submission Date: 12 March 2002
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Institution: University of Pittsburgh
Schools and Programs: Swanson School of Engineering > Chemical Engineering
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: Alumina-supported cobalt catalysts; CO hydrogenation; Cobalt-support compound formation; Fischer-Tropsch synthesis
Other ID:, etd-03122002-155111
Date Deposited: 10 Nov 2011 19:32
Last Modified: 15 Nov 2016 13:37


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