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Metal oxide nanofibres scrub sulphur from petroleum-based fuels

18 December 2012

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

Such efficiency could lower costs and improve performance for fuel-based catalysis, advanced energy applications and toxic gas removal. The work was carried out by Professor Mark Shannon (recently deceased) and Professor Prashant Jain.

Sulphur compounds in fuels cause problems on two fronts: they release toxic gases during combustion, and they damage metals and catalysts in engines and fuel cells. They are usually removed using a liquid treatment that adsorbs the sulphur from the fuel, but the process is cumbersome and requires that the fuel be cooled and reheated, making it less energy efficient.

To solve these problems, researchers have turned to solid metal oxide adsorbents, but those have 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. They lose 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. The solution: tiny grains of zinc titanate spun into nanofibres, combining high surface area, high reactivity and structural integrity in a high-performance sulphur adsorbent.

The nanofibre material is 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. Furthermore, the fibrous structure grants the material immunity from the problem of sintering, or clumping, that plagues other nano-structured catalysts.

“Our nanostructured fibres do not sinter,” 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.”

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