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Effects of CO2 to deactivation behaviors of Co/Al2O3 and Co/SiO2 for CO hydrogenation to hydrocarbons

Abstract

Different deactivation behaviors of the prototype Co/γ-Al2O3 (CoAl) and Co/SiO2 (CoSi) under an excess CO2 environment were investigated in terms of the surface oxidation and aggregation of cobalt crystallites for Fischer-Tropsch synthesis (FTS) reaction. The presence of excess CO2 in the syngas feed largely altered the catalytic activity and product distribution, especially on the CoAl catalyst. A relatively faster deactivation and lower C5+ selectivity under an excess CO2 environment were observed on the CoAl compared with the CoSi, which were fairly stable at same reaction conditions. From the measurement of the reduction-oxidation behaviors of cobalt crystallites, CO2 molecules acted as a mild oxidant by partially oxidizing the exposed metallic cobalt surfaces. A dramatic decrease of CO conversion and increase of CH4 selectivity under CO2 environment over the CoAl was mainly attributed to an irreducible oxidation of the metallic cobalt surfaces through strong interactions with Al2O3 support. Meanwhile, a marginal deactivation rate and less changes of selectivity on the CoSi were mainly attributed to a reversible oxidation-reduction property of the metallic cobalt crystallites by forming larger cobalt crystallites with relatively weak interactions with the SiO2 support. An excess exposure of mild oxidant of CO2 on the FTS catalysts generally decreased the catalytic activity irreversibly by forming strongly interacted large cobalt crystallites, which was more dominant on the acidic Co/Al2O3 than Co/SiO2 catalyst. The easy reversibility of oxidation-reduction of the surface metallic cobalt crystallites on the SiO2 even under the excess CO2 presence can prevent the catalyst deactivation during FTS reaction.

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Publication details

The article was received on 26 May 2017, accepted on 11 Aug 2017 and first published on 11 Aug 2017


Article type: Paper
DOI: 10.1039/C7CY01065F
Citation: Catal. Sci. Technol., 2017, Accepted Manuscript
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    Effects of CO2 to deactivation behaviors of Co/Al2O3 and Co/SiO2 for CO hydrogenation to hydrocarbons

    K. S. Park, K. Saravanan, S. Park, Y. Lee, K. Jun and J. W. Bae, Catal. Sci. Technol., 2017, Accepted Manuscript , DOI: 10.1039/C7CY01065F

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