超老的文章了
但是我觉得只要中国人,印度人,巴西人还要发展,就要铂金做汽车,搞化工
Catalytic-converter production in Shanghai: global demand for the units is
surging.Catalytic-converter production in Shanghai: global demand for the
units is surging.JOHNSON MATTHEY PLATINUM 2004
Lovers may adore platinum's silvery sheen in their favourite jewellery —
but at least they can switch to gold or silver if the price isn't right.
Chemical engineers wish they had the same option.
Thanks to their role in catalytic converters, platinum, palladium and
rhodium have all become crucial bulwarks in the fight against air pollution.
Platinum and palladium can catalyse reactions that convert hydrocarbons and
carbon monoxide into carbon dioxide and water vapour. Rhodium catalyses
another reaction, converting nitrogen oxides into nitrogen and oxygen. These
reactions are at the heart of the three-way catalytic converters now fitted
on almost all cars in the developed world and on an increasing share of
those in India, China and elsewhere.
Although materials such as gold and nickel can perform similar tricks at
lower temperatures, only these platinum-group metals can do the job at the
high pressures and temperatures of 900 °C or more that are found in vehicle
exhaust systems. With demand from the global automobile industry pushing
prices ever higher and no alternative catalysts on the immediate horizon,
car manufacturers are now locked in a race to make each ingot go a little
bit further.
“From a scientific standpoint, the three-way catalytic converter is really
a done deal. It's now an engineering feat to bring the volume of metals down
,” says Johannes Schwank, a chemical engineer at the University of Michigan
in Ann Arbor.
Chemical engineers are working on the problem at the molecular level, trying
to make the catalyst layers even thinner and diluting them with cheaper
alloys. Equally important is the design of the underlying structure to which
the catalysts are applied — although the location of the catalytic
converter and engine design can also play parts. The competition is taking
place largely beyond the academic eye in industrial labs around the world.
Catalytic converters were first put into use in the 1970s after the world's
first regulations on car emissions came into effect in California.
Automobile firms in the United States developed the technology based on
advances in surface chemistry made during the previous decade.
General Motors, Ford and Chrysler were all involved in the development of
the catalytic converter, which Schwank regards as one of the greatest
achievements in the history of chemical engineering. He compares the
hydrocarbon, carbon monoxide and nitrogen oxide molecules in the converters
to helicopters trying to land on the roof of a hospital; the electrochemical
properties of platinum, palladium and rhodium provide an ideal landing pad.
Other elements might not allow them to land at all, or might “hold them
hostage” after their arrival, he says. “The strength of the bonds is just
about right to carry out the reactions, but not so strong that the reaction
agents won't have a chance to leave.”
At first, car makers relied on platinum for this function, but eventually
switched to its sister metal, palladium, at one-third of the price. When
palladium prices spiked in 2000, they went back to platinum, but the cycle
has now repeated itself. Platinum prices are approaching US$1,500 per troy
ounce (this historic measure of precious metals is the equivalent of about
31 grams); palladium costs less than $400.
The recent march of car makers back to palladium has helped to moderate the
price of platinum, as has slower demand from jewellers, according to Johnson
Matthey, a leading catalyst-making firm based in London. However, platinum
performs better than palladium in diesel exhaust systems.
Global platinum supplies stood at more than 7.6 million troy ounces in 2006,
66% of which was used in autocatalysts, according to Johnson Matthey. Those
figures include the recovery of 855,000 troy ounces of platinum from
recycled autocatalysts, which provided 11% of overall global demand. South
Africa supplied 78% of the world's new platinum in 2006 and is home to the
only mines in which platinum is a primary product. For the decade ending in
2006, platinum production increased by more than one-third — but demand for
autocatalysts more than doubled.
Platinum and palladium can play off each other, but manufacturers have to
pay whatever the market demands for rhodium, for which there is no
alternative. Posted at around $6,500 per troy ounce — almost eight times
the price of gold — rhodium is one of the most expensive elements on Earth.
A staggering 87% of the world supply goes into autocatalysts.
Jeremy Coombes, an analyst for Johnson Matthey, says that the amounts of the
metals used in each catalyst depend on the size of the car, the kind of
fuel being used and the local air regulations, and can range from 1–2 grams
for a small car in a lightly regulated environment to 12–15 grams for a
big truck in the United States. That translates to anywhere from $25 to a
few hundred dollars per vehicle, he says: a significant amount for the likes
of Toyota, which sold 2.5 million vehicles last year.
Autocatalysts often use honeycomb-like structures to create vast surface
areas — equivalent to perhaps a couple of football pitches in each
converter — in which reactions can take place. The catalysts are layered as
thinly as possible, often by dipping a ceramic structure into a solution of
the metal. The gradual agglomeration of metal particles under intense heat,
eventually reducing the surface area and catalyst efficiency, is one of
catalyst designers' main challenges.
Nissan announced in August that it has deployed a new fabrication method
that uses nanotechnology to reduce agglomeration. The company claimed the
technique would halve the use of precious metals in its catalytic converters
. Mazda said last month that it can now embed nanoparticles made of platinum
-group metals into ceramic spheres, cutting use “by 70–90% with the same
level of purifying efficiency”. But no public data are available to verify
these claims.
“There is simply not enough platinum and rhodium.”
Although few see prospects for replacing platinum-group metals in catalytic
converters, researchers are searching hard for alternatives in applications
that use low-temperature catalysis. Designers of fuel cells, which catalyse
hydrogen and oxygen to produce electricity and water vapour, are eagerly
seeking cheaper alternatives to platinum. And Schwank says that nickel has
shown promise as a catalyst for onboard fuel reforming, a technique for
generating hydrogen from fossil fuels for use in fuel cells.
And although advances in catalyst design are likely to further reduce the
amount of platinum, palladium or rhodium needed in each vehicle, those gains
might not be enough. Global automobile production has risen from 56 million
vehicles in 2000 to more than 66 million last year and it shows no signs of
slowing, according to the consulting firm Global Insight in Waltham,
Massachusetts.
“There is simply not enough platinum and rhodium going round on this planet
to satisfy the collective demand of automotive emission-control systems and
all of these other areas,” Schwank says. Supply is sure to follow demand
upwards in years to come, but few analysts expect it to get out in front,
and pull prices down. That will leave new technologies that need the
platinum-group metals, such as fuel cells, paying a heavy price for
autocatalysts' insatiable appetite for them.