Catalytic Decomposition of a Perfluorinated Carbon Proxy Using Alumina-based Catalysts

Alumina (Al2O3) from a range of sources have been investigated as potential catalysts for the destruction of fluorocarbon gases produced in the aluminium smelting process. Alumina is the feed used in aluminium production and contains Lewis acid sites on its surface. Under calcined aluminas, such as the transitional γ-Al2O3, contain higher surface areas and more Lewis acid sites on the surface, compared to the fully calcined α-Al2O3. At elevated temperatures (>400 ℃), the surface hydroxyls are released which creates coordinatively unsaturated sites (CUS) on the surface. The surface of potential catalysts were then analysed to quantify the acid sites on the surface of the catalyst (as catalysis is believed to be underpinned by Lews acidity). Surface analysis methods were deployed to determine the speciation on the surface of the catalyst (XPS) and semi-quantitatively determined the proportion between strong and weak acid sites (NEXAFS). Surface analysis methods were deployed to determine the phases present in the catalyst (XRD). Quantitative acid site calculations used thermogravimetric analysis (TGA) and back-titration methods. Potential catalysts were then tested to decompose SF6 using a custom-made rig. SF6 was used as a proxy to PFC’s as both produce a key decomposition product (HF) and are completely fluorinated (which leads to both being inert and potent as greenhouse gases). Therefore, the performance of the alumina-based catalyst in the decomposition of SF6 provided insight into how well the catalyst would perform in the presence of PFC’s. Using these methods, alumina derived from an industrial, commercial Bayer-gibbsite (ABG) was found to decompose PFC’s at a high % conversion. Above a threshold temperature of 500 ℃, an increase in reaction temperature produced higher catalyst performance (up to 700 ℃). Alumina derived from laboratory-grade gibbsites, prepared by calcination of laboratory grade reagents, were found to exhibit higher SF6 % conversion than ABG samples. The experiments undertaken demonstrate that alumina catalysts are a viable method of PFC destruction in conditions that allow the surface to be dehydroxylated. It is possible that these conditions are already replicated in certain regions of an aluminium reduction cell which bodes well for future in-situ application.

Name thesis:degree_name

PhD

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Chemistry

Grantor dc:publisher

ResearchSpace@Auckland

Year dc:date.issued

2022

Author dc:creator

• Camacho, Luis Miguel Ealdama

Advisors dc:contributor.advisor

• Metson, James
• Waterhouse, Geoffrey

Statement dc:rights

• Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated.

Licence dc:rights.uri

• https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm

Handle dc:identifier.uri

https://hdl.handle.net/2292/61334

OAI identifier oai:identifier

oai:researchspace.auckland.ac.nz:2292/61334