Aqueous Fischer-Tropsch is clean and green

12 December 2007

Chinese chemists have carried out the Fischer-Tropsch (FT) reaction in water for the first time, bringing a greener route to hydrocarbon fuels a step closer. 

FT produces short-chain hydrocarbons by hydrogenation of carbon monoxide over a metal catalyst - usually iron or cobalt. The catalyst is usually supported on carbon or silicon dioxide to optimise its activity.

Now a team from Peking University (PKU), China, has used a different approach - catalysing the reaction in water using 2nm clusters of ruthenium, stabilised by PVP, a water-soluble polymer. The unsupported catalyst is more active than conventional catalysts and so the reaction runs well at lower temperatures. 

The researchers saw a 35-fold increase in activity over supported catalysts at a standard operating temperature of 150°C, and a 16-fold increase at only 100°C. 

The aqueous-phase Fischer-Tropsch synthesis achieves higher activity than conventional supported catalysts © C-X Xiao et al, Angew. Chem.

The hydrocarbon product also doesn't mix with water, so the resulting fuel is uncontaminated by the catalyst. All these points are key to a 'green' reaction, an important concern in synthetic chemistry - especially where the product is a potential replacement for petroleum. 

'The [FT] synthesis became "classical", and its concept has been widely accepted as successful - including its advantages and disadvantages,' Kou Yuan, professor at the PKU Green Chemistry Centre and co-author of the paper, told Chemistry World. 'We have criticised this 80-year-old process for years due to its very old catalyst design and complex operation.' 

The work also raises questions about the current thinking on supported catalysts, according to Kou. The results 'imply that the functions of supports are perhaps misinterpreted in the current catalytic community,' he said. 

Commenting on the findings, Peter Maitlis, emeritus professor of chemistry at the University of Sheffield, said, 'If the results described in the paper can be reproduced by other workers, it represents an interesting and exciting development. The economics are clear, however - ruthenium is too expensive to be used on an industrial scale, and they'll have to show that they can also do it with the much cheaper conventional FT catalyst: iron.' 

Jonathan Edwards

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References

Xiao et al, Angew. Chem. Int. Ed., 2007, DOI: 10.1002/anie.200703481

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