In BASF's catalyst testing facility in Union, New Jersey, USA,
experts check the installation of a catalyst underneath a test
vehicle.
BASF researchers improve cleanup of diesel
emissions
There are currently more than half a billion cars on the roads
worldwide, plus around 200 million trucks. Although this intense
automobile traffic raises many environmental issues, health
hazardous exhaust gases do not necessarily have to be one of them.
In theory, the hydrocarbons in the gasoline are combusted with
atmospheric oxygen to give the nontoxic end products carbon dioxide
and water. In the real world of the automobile this ideal
combustion process is not that easy to accomplish. Incomplete
combustion and the presence of minimal impurities in the fuel can
result in the formation of toxic carbon monoxide, unburned
hydrocarbons, nitrogen oxides and for diesels carbon particulates
(soot). When optimally adjusted, modern engines can reduce
emissions of these pollutants significantly. The key to clean
exhaust gases, however, lies in the conversion of the harmful
emissions into harmless end products by catalytic converters. The
widespread introduction of such catalytic converter systems in
North America (starting in 1976) and Europe (1986) resulted in a
marked decrease in metropolitan air pollution from harmful tailpipe
emissions despite a growing population of vehicles.
The development of the first three-way catalytic converter by
the US American company Engelhard in 1979/80 marks a milestone in
exhaust gas technology. This device was able to catalyze the
conversion of the three main pollutants (unburned hydrocarbons,
carbon monoxide and nitrogen oxides) simultaneously. "Ever since,
Engelhard's researchers have remained among the leading innovators
in this field and are continuing their successful work following
the integration into BASF", emphasizes Dr. Bob Farrauto, Research
Fellow at BASF Catalysts LLC in Iselin, New Jersey.
In the engine laboratory catalysts are subjected to long term
stress testing. The electronic measuring equipment records all the
emission values.
As a general principle, a catalyst allows chemical conversions
to desired products to occur more rapidly and at lower
temperatures. For this reason, in addition to pollution control,
industrial catalysts find use in a wide field, be it the processing
of petroleum to produce transportation fuels or the production of
chemicals including polymers and pharmaceuticals. Ideally, the
catalyst itself is not chemically consumed during this process.
Automotive emissions catalytic converters consist of special
combinations of precious metals such as platinum, palladium and
rhodium dispersed on high surface area carriers which in turn are
coated onto the walls of ceramic or metallic monolithic structures.
In the modern three-way catalytic converter, uncombusted fuel
residues are oxidized with oxygen to produce carbon dioxide and
water, nitrogen oxides are converted to ubiquitous nitrogen, and
toxic carbon monoxide is oxidized with oxygen to carbon dioxide.
Like this, a typical catalytic converter is capable of destroying
around 98 percent of hydrocarbons, carbon monoxide and nitrogen
oxides produced by the car's engine.
"The principle of a catalyst may be simple, but it's the details
of the technological implementation that cause the headaches",
explains Bob Farrauto. "The catalyst needs the right operating
temperature and an accurately adjusted residual oxygen content in
the exhaust gas." In today's catalytic converters, the oxygen
content is measured and regulated by lambda sensors. Through a
computer controlled feedback system the mixture of air and fuel
entering the engine is adjusted to meet the requirements for the
three-way catalyst to function.