Generation of catalytic films on aluminium supports by plasma electrolytic oxidation methods (PEO)

UoM administered thesis: Phd

  • Authors:
  • Chaozhou Li

Abstract

Plasma electrolytic oxidation (PEO) is an emerging surface treatment technology of special interest for the generation of corrosion- and wear-resistant coatings on aluminium and its alloys. The oxide coatings are formed in aqueous electrolytes under high applied voltages. This technology enables the generation of coating of up to tens of microns in thickness containing various crystalline alumina phases. The PEO coating are of interest as potential alternatives to gamma alumina powder, which is one of the most commonly used catalysts/supports in industry. Alumina films were produced on aluminium plates (0.3mm thick, 99.9% purity) and aluminium wires (diameter 1mm, 99.5% purity) using PEO within an alkaline electrolyte solution. Unlike the typical PEO coating which was designed for metal corrosive protection, an evenly oxidised film covered the whole substrate with a large surface area (porosity) was required to be considered as a catalyst support. Therefore, several parameters (such as anodic to cathodic ratio, current density and frequency) were altered during the PEO coating synthesis to modify the oxide coating morphology and composition. The produced alumina was characterised using scanning electron microscopy, energy dispersive X-ray analysis and X-ray diffraction. The mixed phase alumina layer on aluminium plates/ wires were utilized as structured catalysts in methylcyclohexane (MCH) dehydrogenation after platinum metal was dispersed on the surface. MCH dehydrogenation was used as it is a well-known, facile, endothermic catalytic reaction and can be carried out over both homogenous and egg shell platinum dispersed catalysts. The traditional pelletised Pt-loaded alumina was tested in MCH dehydrogenation for comparison. The catalytic products over structured catalysts prepared by PEO coating were similar to traditional pelletised catalysts. Although the selectivity to toluene for both types of catalysts was similar, the MCH conversion of structured catalyst was much lower initially using a plate geometry. However, when using wires to improve packing, the conversion of optimised PEO coating improved and was comparable to traditional catalyst. Platinum dispersion remained key to a better catalyst, although alternative platinum loading methods, such as, sputter coating and deposition using plasma were attempted.

Details

Original languageEnglish
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Award date1 Aug 2019