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Formation of 2-alkenes as secondary products during Fischer–Tropsch synthesis

Paper ID Volume ID Publish Year Pages File Format Full-Text
39543 45826 2015 6 PDF Available
Title
Formation of 2-alkenes as secondary products during Fischer–Tropsch synthesis
Abstract

•There is an inverse isotope effect during Fe catalyzed FT reactions.•The KIE during FTS over iron catalysts (αH/αD) is 0.88 at 270 °C.•1-alkenes and 2-alkenes are formed through two different pathways during FTS.•There is a normal isotope effect in the formation of 2-alkenes during FTS at 270 °C.•Internal alkenes produced during FTS are products of secondary reactions.

The H2/D2 switching experiments showed that there is an inverse isotope effect during iron catalyzed Fischer–Tropsch (FT) reactions. The rate of hydrocarbon production (r) increased when syngas CO/H2 was switched to CO/D2 with the ratio of rH/rD being 0.55–0.58. The inverse isotope effect in every propagation step was calculated to be 0.88, which is a reasonable value for an inverse isotope effect at 270 °C that originates from the C–H (D) bond hybridization change from sp2 to sp3. These results are similar to cobalt catalyzed FT reactions that were explained by the modified alkylidene mechanism by which 1-alkenes and n-alkanes are the primary products of the FT reaction and the others are products of secondary. The detailed analysis of products produced during iron catalyzed FT reactions with CO/H2 or CO/D2 as the syngas feeds showed that while the ratios of [1-alkenes]H/[1-alkenes]D are less than 1, the ratios of [2-alkenes]H/[2-alkenes]D are more than 1; this indicates that 2-alkenes are produced through a pathway that is different from 1-alkenes. These results also suggest that there is a normal isotope effect during the formation of 2-alkenes through the corresponding 1-alkenes, which will result in the ratio of [1-alkenes]H/[1-alkenes]D being less than 1. The formation of 2-alkenes is explained by the alkylidene mechanism.

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Keywords
Fischer–Tropsch reaction; Inverse isotope effect; Alkylidene mechanism; Formation of 2-alkenes; Deuterium tracer
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Formation of 2-alkenes as secondary products during Fischer–Tropsch synthesis
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis A: General - Volume 490, 25 January 2015, Pages 201–206
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
Get Full-Text Now
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Price was $35.95
You save - $31
Price after discount Only $4.95
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Full-text PDF Download
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