Republic of Ireland Regional Group

SCI Members' News

Greener approach to catalysts in fuel production

Scene of the future: hydrogen refueling dispenser and car (image: Ovonic Hydrogen)

In recent years, the annual general meeting of the Republic of Ireland Group has had a green theme, aimed at the general public, and it has been several years since the group hosted a technical talk aimed primarily at chemists. A recent article in Chemistry and Industry (C&I 2006, 16, 22) prompted the group to organise a lecture that preserved the environmental focus and which brought a welcome return to scientific presentations. In Trinity College Dublin, on 19 October 2006, Malcolm Green of the Inorganic Chemistry Laboratory, Oxford University, discussed ‘Catalysts for green fuels – save the world maybe’.

Green’s thesis was that the hydrogen economy, as currently posited, cannot deliver significant reductions in carbon dioxide emissions in the short term because of the difficulties in transporting and storing hydrogen gas.

His proposal was to produce hydrogen in large installations using nuclear or renewable energy, but then to convert it into hydrocarbons, which are much easier and cheaper to transport, either as gas (methane) or liquids. Hydrogen can then be produced again in situ for use in fuel cells by reforming the hydrocarbons. Since the production of hydrocarbons would use up carbon dioxide the proposed cycle would be at worst carbon neutral. And new catalysts are making this approach increasingly attractive.

The idea is that hydrogen should be obtained from water, either by electrolysis at nuclear power stations, at huge wind farms built away from population centres, or thermally at solar installations. Hydrogen can also be extracted in the form of synthesis gas (hydrogen plus carbon monoxide) from biomass by partial oxidation. Some of this hydrogen can then be used to reduce atmospheric carbon dioxide to more carbon monoxide by the reverse shift reaction. It is then possible to produce hydrocarbons from carbon monoxide and hydrogen using Fischer-Tropsch synthesis. In a car, hydrogen and carbon monoxide can be recovered by partial oxidation. The hydrogen would be ‘burnt’ electrochemically in a fuel cell, while the carbon monoxide would either be burnt conventionally in a hybrid combustion/low temperature fuel cell vehicle, or electrochemically with a high temperature fuel cell.

An early catalyst for the production or oxidation of methane is the pyrochlore Ru₂Sn₂O₇, but this is very expensive. Green’s team found that this could be achieved much more cheaply (albeit at low throughput) with a molybdenum carbide (Mo₂C) catalyst, and latterly (and even more successfully) with a cobalt carbide catalyst. What is now needed is a selective catalyst to allow these reactions to make or ‘burn’ higher alkanes such as octane.

A largely technical audience enjoyed an informative yet amusing talk, and also the traditional enzymatic oxidation of a few beakers of aqueous bioethanol afterwards.

David Birkett,
Republic of Ireland Group Secretary