Text

theses

In order to achieve the process from nitrogen and hydrogen to ammonia under mild conditions thus save energy cost, possible intermediates have to be located and good catalysts need to be found. Hydrazine (N2H4) is believed to be one of the intermediates in this process. This thesis aims to find a comparatively good catalyst towards hydrazine to establish a potential catalytic nitrogen fixation cycle. At the very beginning of this project, a preliminary screening was done to locate a potentially good catalyst towards hydrazine. The pincer rhodium fragment gave promising result: disproportionation ratio products (N2 and NH3) were achieved in comparatively short time under room temperature. A mechanism of this disproportionation reaction was then calculated. It contains of two pathways: hydrogenation and dehydrogenation. The calculated barriers show that dehydrogenation should be slower than hydrogenation. Thus the supply of hydrogen to the hydrogenation pathway is constrained. Reactions under hydrogen atmosphere proved this result. And also, kinetic studies were done to partially prove the calculated mechanism. When the reaction was carried out with pincer rhodium hydridochloride as the catalyst precursor, base (NaOtBu) was needed to provide the 14 electron speices to start the catalytic cycle. It was found that reactions under more base gave less ammonia with similar reaction rate. This means hydrogenation pathway was hindered under basic condition. Then reactions with substituted hydrazines were done to stop the reaction at the diazene stage to prove the calculated dehydrogenation pathway. In these reactions, C-H activation and double N-H activation on the same nitrogen atom were observed.

ETD_6291

M.S.

Includes bibliographical references

by Jia Song

doi:10.7282/T3HX1FHJ

ETD graduate

The author owns the copyright to this work.