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Stimulation of catalytic activity of transitional metal nitrides and carbides

Cassidy, Brett (2017) Stimulation of catalytic activity of transitional metal nitrides and carbides. Honours thesis, Murdoch University.

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Current estimations show hydrogen production to be in excess of 55 million tonnes annually. With consumption growing globally by six percent annually, new feedstocks such as ammonia need to be explored to meet demand. Ammonia has many attractive characteristics as a source for hydrogen, such as its product stream when decomposed producing no carbon oxides or sulfurs. Research currently is limited on the decomposition of ammonia to produce hydrogen supported by transitional metal catalysts. This lack of research has suppressed the development of this technology. This thesis project is intended to develop on the original research conducted at the King Abdulaziz University where the development of high surface area molybdenum nitride was researched as a catalyst for the ammonia decomposition reaction to produce hydrogen.

The work completed in this thesis aims to capitalise on the findings in the original experiment by accurately determining the mechanisms and kinetics associated with the production of hydrogen. The modelling was separated into three distinct components which investigated the ammonia decomposition on a cobalt-molybdenum catalyst. The first component of the model was focused on optimising the surface which the mechanisms of the decomposition reaction would be situated on. The optimisation calculations found the (111) index to be the most stable of all the surfaces modelled. The data collected displayed a directly proportional relationship between the increasing number of atoms in the structure and its stability. The second component of the project modelled the ammonia decomposition mechanisms on the surface of the optimum (111) indexed surface. Multiple iterations were tested for different locations of the reacting molecule above the surface of the catalyst. The results from the optimised models found the desorption mechanisms were slightly more stable than the adsorption component of the decomposition reaction.

The concluding component of the model investigated the transient states associated with the ammonia decomposition reaction. Six transient states where identified, however only five could be modelled as a result of an atomic imbalance between the adsorption and desorption phases. Multiple transient states were calculated, with the rate limiting step determined to be the final desorption of the hydrogen molecule from the catalyst surface. From the transient state models it was determined that the Co3Mo3N catalyst was kinetically unsuitable for the ammonia decomposition reaction.

Item Type: Thesis (Honours)
Murdoch Affiliation(s): School of Engineering and Information Technology
Supervisor(s): Altarawneh, Mohammednoor
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