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Fischer-Tropsch Synthesis on ZrO2-promoted Co/Al2O3 Catalysts: Effect of Catalyst Support Preparation Methods
KTH, School of Chemical Science and Engineering (CHE).
2016 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesisAlternative title
Fischer-Tropsch syntes med ZrO2-promoted Co/Al2O3 katalysatorer : Effekten av olika framställningsmetoder av katalysatorbärare (Swedish)
Abstract [en]

Alumina is considered to be an effective catalyst support in the Fischer-Tropsch synthesis, owing to its favourable mechanical properties. However, if cobalt is deposited over alumina, the formation of active phase-support species decreases the catalyst reducibility and can be detrimental to the reaction performance. Recently, according to some reports, zirconia has attracted attention as a cobalt catalyst promoter for improving reducibility, activity and C5+ selectivity.

This experimental work is aimed at studying the influence of zirconia promotion on cobalt-based catalysts. Two different support preparation methods were investigated: the pH-controlled precipitation of the zirconia promoter over a gamma alumina carrier from a one-phase and from a microemulsion solution. Two microemulsion systems were used: the water-in-oil and the oil-in-water techniques. The zirconia loading target over alumina was 20 wt% for all the promoted carriers. The cobalt active phase was deposited via the incipient wetness impregnation, reaching a concentration of 12 wt% over all the catalysts, including on a non-promoted one. Moreover, a further support was prepared using the oil-in-water microemulsion technique and impregnated with 15 wt% Co.

X-ray diffraction, N2 adsorption and H2 chemisorption characterisations revealed comparable catalyst porosities and cobalt dispersions. Furthermore, TPR analyses showed that reducibility is not influenced by the addition of zirconia.

The catalyst activation treatment was performed under pure hydrogen at 1 atm, 350 °C for 16 h. The syngas flow, passing through a fixed bed reactor, was first set to 250 NmL/min and then decreased until 30%, 40% and 50% CO conversion values were reached. The catalytic test results revealed an increase in activity and enhancement of C5+ selectivity for the catalyst prepared by pH-controlled precipitation of zirconia from the ordinary solution, relative to the non-promoted one. On the other hand, the “microemulsion” catalysts showed a significant decrease in turnover frequency compared to the Co/Al2O3 catalyst performance. Selectivity to C5+ and CH4 were respectively enhanced and reduced by promoting the catalyst with zirconia, for each conversion step. Olefin-to-paraffin content ratio in the fraction of C2, C3 and C4, along with the deactivation trend, were also analysed and discussed.

Place, publisher, year, edition, pages
2016. , 110 p.
Keyword [en]
Fischer-Tropsch synthesis, Co/Al2O3, zirconia promotion, activity, reducibility
National Category
Chemical Process Engineering
Identifiers
URN: urn:nbn:se:kth:diva-190913OAI: oai:DiVA.org:kth-190913DiVA: diva2:953707
Available from: 2017-05-15 Created: 2016-08-18 Last updated: 2017-05-15Bibliographically approved

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