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Overcoming sulphur contamination

Some metals are used as catalysts to help facilitate chemical reactions. Fuel cells for example use platinum to help generate energy from the fuel.

Sulphur is a contaminant in many types of fuels and can attach to the surface of the metal particles. This can cause the reactions to slow down or stop completely, resulting in severe costs due to the downtime needed to replace or reactivate the catalyst. It has been difficult to determine how sulphur bonds to the metal, and therefore how it blocks the catalytic process.

Katja Eder employed the nanoscale resolution of flagship atom probe tomography (APT) at Microscopy Australia’s University of Sydney facility, Sydney microscopy and Microanalysis, to analyse sulphur–metal bonding for the first time. Needle-shaped specimens with a tip diameter of less than 100 nm were prepared from the common catalysts tungsten, platinum and aluminium.

They were then dipped in a sulphur-containing compound, under controlled atmosphere in a specially designed transfer system to ensure no oxygen was present to oxidise the metal. This generated a tip coated with a single layer
of sulphur.

Analysis revealed that different metals bound sulphur quite differently. Bonding was also affected by surface oxidation. Understanding the conditions that affect how sulphur bonds to different metals will enable researchers to design composite nanoparticles that could modulate how strongly sulphur bonds to the surface. This could improve catalytic performance and maximise the particles’ functional life. This in turn can influence the effectiveness and economic viability of fuel cells and other catalytic devices.

Eder, K., et al. (2017). A New Approach to Understand the Adsorption of Thiophene on Different Surfaces: An Atom Probe Investigation of Self-Assembled Monolayers. Langmuir 33(38): 9573-9581.

3D APT reconstruction showing the atomic distribution at the tip of a sulphur-coated tungsten specimen. Sulphur is red, tungsten is grey and oxidised tungsten is green.