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Title: Cobalt rhenium catalysts for ammonia synthesis
Author: McAulay, Kate
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 2017
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Cobalt rhenium ammonia synthesis catalysts which are highly active at ambient pressure and 400°C under N2/H2 (1:3) have been prepared without an ammonolysis step. For all highly active cobalt rhenium materials the post-reaction powder XRD patterns reveal there is a shift of their Re reflections to a slightly higher 2θ angle. This shift is due to mixing of cobalt and rhenium within the material and this interaction was confirmed via XAS analysis. The XRD patterns of cobalt rhenium materials with minimum ammonia synthesis activity resemble the reference pattern for metallic rhenium and show no signs of bimetallic mixing. Cobalt rhenium materials have been benchmarked against CsNO3 doped Ru/Al2O3 materials. Pre-treatments under N2/H2 (1:3), Ar/H2 (1:3), N2 and Ar gas mixtures have been shown to influence catalytic performance, with the first resulting in an instantly active material, whereas, the others lead to a 20 minute induction period prior to the development of activity upon switching to an ammonia synthesis feedstream. Also, pre-treatment in N2/H2 (1:3) resulted in a material with higher catalytic activity. CoRe4 was studied via in situ XAS/XRD to elucidate the reducibility and local environment of the two metals during reaction conditions. The phases present in the CoRe4 catalyst during ammonia production are largely bimetallic Co-Re and also monometallic Co and Re species formed during both pre-treatments. It was found the presence of nitrogen during the pre-treatment strongly promotes the mixing of the both Co and Re. Preliminary tests were also conducted on cobalt rhenium catalysts for ammonia decomposition and the materials were found to have high activity. To the author's knowledge this is the first report of low surface area materials being particularly active for this reaction.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QD Chemistry