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Investigation of the highly tunable selectivity to linear α-olefins in Fischer-Tropsch synthesis over silica supported Co and CoMn catalysts by carburization-reduction pretreatment

Abstract

The evolutions of metallic Co through RCR treatment and during FTS reaction have been comparatively investigated considering the effects of Mn promoter and varied conditions. The results show the selectivity to α-olefins can be fine-tuned. In detail, the Co3O4 (311) is always firstly reduced to metallic Co (111) followed by carburization with CO to form Co2C (111). However, second reduction over Co2C (111) results in Co (101) and Co (002) for 15Co/SiO2-RCR. In contrast to un-modified 15Co/SiO2, the addition of Mn alters the evolution of Co2C (111) into Co (101) and Co (100) for 15Co3.7Mn/SiO2-RCR. During FTS reaction over R-treated catalysts, the Co (111) is kept almost unchanged for 15Co/SiO2-R, but gradually evolves into Co3C (101) over 15Co3.7Mn/SiO2-R. For comparison, the 15Co3.7Mn/SiO2-RCR exhibits the stable Co (101) and Co (100) in FTS reaction. The above evolutions reflect a marked effect on the catalytic performance. The Co (101) and Co (002) display a notable increase in the selectivity to total olefins compared to that for Co (111). Furthermore, the abundant experiments also reveal that the Co3C (101) is favorable for olefins, especially lower olefins with a low selectivity to methane, however, the Co2C (111) shows a negligible activity with un-desired high selectivity to methane. From the comprehensive experimental data, the selectivity to total olefins might be mainly affected not only by Co phase state and crystal facet but also by unpaired d-orbital electron number modified with Mn and the H2/CO ratio in feed gas, etc, directly determining the ratio of H*/C* on the catalyst surface. As an optimal result, an excellent selectivity of 74.2% in total olefins is obtained. In addition, the olefin distributions could be efficiently tailored by simply changing the reaction temperature.

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Publication details

The article was accepted on 15 Sep 2017 and first published on 15 Sep 2017


Article type: Paper
DOI: 10.1039/C7CY01764B
Citation: Catal. Sci. Technol., 2017, Accepted Manuscript
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    Investigation of the highly tunable selectivity to linear α-olefins in Fischer-Tropsch synthesis over silica supported Co and CoMn catalysts by carburization-reduction pretreatment

    J. Zheng, J. Cai, F. Jiang, Y. Xu and X. LIU, Catal. Sci. Technol., 2017, Accepted Manuscript , DOI: 10.1039/C7CY01764B

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