Thesis
Conversion of polyethylene into high value carbon nanomaterials
- Creator
- Rights statement
- Awarding institution
- University of Strathclyde
- Date of award
- 2026
- Thesis identifier
- T18038
- Person Identifier (Local)
- 202073265
- Qualification Level
- Qualification Name
- Department, School or Faculty
- Abstract
- Plastic waste accumulation poses a major environmental challenge, with conventional recycling strategies insufficient to address its scale. Chemical upcycling of polyolefins into carbon nanomaterials (CNMs) offers a promising valorisation route, with one-stage direct pyrolysis offering a simplified reactor configuration. However, direct exposure of catalysts to complex plastic-derived intermediates under these conditions increases susceptibility to deactivation and uncontrolled carbon deposition. The performance and mechanistic behaviour of transition metal catalysts under these conditions remain insufficiently understood. This thesis aims to elucidate how catalyst composition and structure affect CNM growth in direct LDPE pyrolysis. Bimetallic and microporous aluminosilicates supported formulations were predicted to outperform conventional monometallic alumina-supported catalysts, due to enhanced nanoparticle stability, carbon-metal interactions, metal-support anchoring and precursor cracking. Catalyst performance was evaluated by CNM conversion, morphology and graphitic quality, along with metal nanoparticle dispersion and support structure. Iron-based exhibited limited activity due to sintering and formation of deactivated phases. Cobalt displayed highest nanoparticle dispersion, forming both carbon nano-onions and carbon nanotubes, while Nickel catalysts displayed a higher selectivity for nanotubes. Contrary to initial expectations, bimetallic formulations did not consistently improve performance relative to monometallic systems. In contrast, secondary metal promoters were effective, with molybdenum optimal for conversion and manganese for graphitic quality. Zeolites outperformed traditional alumina or clay supporting materials, with performance influenced by synergistic effects between metal and support. Ni stabilised the zeolite frameworks, preserving the open three-dimensional pore structures, and thus bulk precursor diffusion and metal nanoparticle dispersion. Whereas, Co induced controlled framework collapse, allowing active metal sites to be exsolved from the restrictive one-dimensional channels, producing small pore-templated accessible surface metal nanoparticles. These results show how catalyst behaviour in single-stage systems differs from multi-stage, and how catalyst performance is governed by metal-support interactions and structural evolution, providing mechanistically informed guidance for future catalyst design.
- Advisor / supervisor
- Zhang, Xiaolei
Relations
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PDF of Thesis T18038 | 2026-08-03 | Public | Download |