Metal oxide nanofibres scrub sulphur from petrol fuels

University of Illinois researchers have developed mats of metal oxide nanofibres that scrub sulphur from petroleum-based fuels much more effectively than traditional materials.

It is claimed that such efficiency could lower costs and improve performance for fuel-based catalysis, advanced energy applications and toxic gas removal.

Co-led by the late Mark Shannon, a professor of mechanical science and engineering at the University of Illinois, and chemistry professor Prashant Jain, the researchers demonstrated their material in the journal Nature Nanotechnology.

Sulphur compounds in fuels release toxic gases during combustion, and they damage metals and catalysts in engines and fuel cells.

According to the university, they usually are removed using a liquid treatment that adsorbs the sulphur from the fuel, but the process is said to be cumbersome and requires that the fuel be cooled and reheated, making the fuel less energy efficient.

To solve these problems, researchers have turned to solid metal oxide adsorbents, but those are said to present their own sets of challenges: while they work at high temperatures, eliminating the need to cool and re-heat the fuel, their performance is limited by stability issues, losing their activity after only a few cycles of use.

Previous studies found that sulphur adsorption works best at the surface of solid metal oxides, so graduate student Mayank Behl, from Jain’s group, and Junghoon Yeom, then a postdoctoral researcher in Shannon’s group, set out to create a material with maximum surface area.

They created tiny grains of zinc titanate spun into nanofibres, uniting high surface area, high reactivity and structural integrity in a high-performance sulphur adsorbent.

The nanofibre material is claimed to be more reactive than the same material in bulk form, enabling complete sulphur removal with less material, allowing for a smaller reactor.

The material stays stable and active after several cycles, and the fibrous structure grants the material immunity from the problem of sintering that plagues other nano-structured catalysts.

In a statement, Jain said: ‘The fibrous structure accommodates any thermophysical changes without resulting in any degradation of the material. In fact, under operating conditions, nanobranches grow from the parent fibres, enhancing the surface area during operation.’

Jain’s group will continue to investigate the enhanced properties of nanofibre structures, hoping to gain an atomic-level understanding of what makes the material so effective.

’We are interested in finding out the atomic sites on the surface of the material where the hydrogen sulphide adsorbs,’ said Jain. ‘If we can know the identity of these sites, we could engineer an even more efficient adsorbent material. The atomic or nanoscale insight we gain from this material system could be useful to design other catalysts in renewable energy and toxic gas removal applications.’