Date of Award

January 2014

Degree Type

Open Access Thesis

Degree Name

Master of Science (MS)

Department

Chemistry

First Advisor

Buchang Shi

Department Affiliation

Chemistry

Second Advisor

Donghui Quan

Department Affiliation

Chemistry

Third Advisor

Darrin L. Smith

Department Affiliation

Chemistry

Abstract

The Fischer-Tropsch Synthesis (FTS) was invented in 1920s, shortly after its invention, it became an important way to produce synthetic fuels. The FTS is also an important way to understand the origin of life. Even though the FTS has been used to produce liquid fuels commercially for a relatively long time, the mechanism of FTS is still unclear, a mechanism can explain all the experimental observations has not been discovered yet.

By conducting H2/D2 switching experiments we found that there was an inverse isotope effect in the Fe catalyzed FTS. The rate of hydrocarbon production was increased when syngas H2/CO was switched to D2/CO. The inverse isotope effect was calculated to be 0.83 to 0.97 for Fe/Si/K runs and 0.71 for Fe/Si catalyzed FTS. These results can be explained by the modified alkylidene mechanism which was proposed based on Co catalyzed FTS studies.

The product analysis of H2/D2 switching experiments of iron catalyzed FTS showed that the ratios of [1-alkenes]H/[1-alkenes]D are less than 1 while the ratios of [2-alkenes]H/[1-alkenes]D are greater than 1, which is indicating that the 2-alkenes were produced through a different pathway from 1-alkenes. The formation pathway of 2-alkenes has been proposed based on the modified alkylidene mechanism.

We also conducted the H2/D2 competitive experiments by using an equal molar ratio of H2 and D2 as the syngas. The results showed that the H/D ratios in alkanes from C8 to C19 were less than 1. It clearly indicates that there is deuterium enrichment during iron catalyzed FT reactions. Unlike Co catalyzed FTS, in which the H/D ratio decreased with increasing carbon numbers, the H/D ratio in iron catalyzed FTS decreased from C8 to C11 and became almost a constant from C11 to C19 during Fe/Si/K runs, while in Fe/Si run the H/D ratio decreased from C8 to C14 and start increasing from C15 to C16. These results can be explained by the modified alkylidene mechanism while other factors need to be taken into consideration.

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