Sweet step to hydrogen revolution

Platinum extracts green fuel from glucose.

Chemists in the United States
have developed a way of
making hydrogen from plant
matter. It is a step towards
hydrogen becoming cheap
and plentiful enough for it to
be used as non-polluting fuel.

PHILIP BALL Nature.com

James Dumesic and
co-workers at the University of
Wisconsin in Madison heated
a glucose solution extracted
from plant tissues to around
200 °C under pressure. They
passed it over a catalyst
comprising tiny platinum
particles scattered throughout
a matrix of porous aluminium
oxide. This process breaks
the glucose down into
hydrogen, carbon dioxide and
small amounts of methane1.

The technique is even more
efficient when methanol is
used instead of glucose.
Methanol and ethanol are already produced as biofuels from
plant sources such as corn and wheat. But hydrogen is a
better, cleaner fuel.

A type of sugar, glucose is manufactured in vast quantities,
for example in corn syrup fermented from corn starch. It
provides large amounts of energy and fuels our own
metabolic processes. Glucose is also the building block for
carbohydrates such as cellulose, which supports plant tissues.

So Dumesic’s team hope that their process might work not
only with refined glucose, but also with waste plant matter
such as wood pulp, straw and stover, the fibrous remains of
corn production.

If it can be produced cheaply, hydrogen could rescue us from
our reliance on fossil fuels. When burnt in air it releases a lot
of energy, and the only by-product is water. Fossil fuels, on
the other hand, generate greenhouse gases such as carbon
dioxide and poisonous carbon monoxide.

Electric vehicles can run on hydrogen using fuel cells to
convert combustion energy directly into electricity. Many
motor companies, including DaimlerChrysler and Ford, have
produced prototype hydrogen-powered vehicles. These are
not widely available, partly because of the difficulty of
procuring hydrogen as a fuel.

Break down

In principle, hydrogen can be made by using electricity to
split water molecules. But this merely shifts the energy
problem elsewhere: the electricity generally comes from a
fossil-fuel power plant.

Hydrogen can also be extracted from glucose by using
pressurized steam, but this is costly. And bacteria break
down biomass, such as sweet potato starch, into hydrogen by
fermentation, but this can be tricky on an industrial scale.

Inorganic catalysts such as platinum are more robust than
bacterial enzymes, and are also amenable to improvements
that give a better yield of hydrogen. Some inorganic catalysts
can produce hydrogen from vegetable oils. But the Wisconsin
process might also work with raw plant fibres.

Dumesic and colleagues admit that they do not yet have an
industrial process on their hands. They need to find a
catalyst that is cheaper than platinum, can handle a wider
range of starting materials, and produces a better yield of
hydrogen – at the moment some of it is squandered in other
reaction products. But they are confident that these
improvements can be made.

References

1.Cortright, R. D., Davda, R. R. & Dumesic, J. A. Hydrogen from
catalytic reforming of biomass-derived hydrocarbons in
liquid water. Nature, 418, 964 – 967, (2002).

© Nature News Service / Macmillan Magazines Ltd 2002

http://www.nature.com/nsu/020826/020826-5.html