Motors has turned to the University of Tulsa in Oklahoma for help developing lean
burn engines with copper zeolite catalysts to meet tough new U.S. emission standards.
Lean burn engines are more fuel-efficient than standard petrol engines because
they burn higher ratios of oxygen to fuel, but they can’t meet new U.S. pollution
standards that will be in effect in three years, says Richard Blint, a senior
research scientist with the chemical and environmental sciences lab at GM’s
research and development centre in Michigan.
The excess oxygen tends to produce oxides of nitrogen that current palladium
and platinum catalytic converters are unable to remove in a lean-burn system.
The research team is researching catalytic materials that will be both durable
and efficient for lean burn engines, including diesels.
Very few catalysts operate lean, and those that do either are not efficient
enough to meet government standards, or do not last long enough to be economically
feasible, according to Blint.
"Lean burn engines provide high efficiencies," Blint says. "However,
the U.S. emissions standards that will be phased in between 2003-2007 are very
stringent. We need a new catalyst technology to be able to use lean burn engines
in a broad spectrum of vehicles."
The research is centered on copper zeolites, says Geoffrey Price, chairman
of Tulsa University’s chemical engineering department and GM’s research
These zeolites are made with aluminum, silicon and copper which is the active
ingredient that promotes the chemical reaction in a catalyst to clean up a vehicle’s
The zeolite, a porous structure, supports the copper and contributes to desired
catalytic properties of copper.
The catalyst is designed to convert nitrogen oxides – components that
can lead to the creation of ozone – into nitrogen and water.
"Copper zeolites as emission control catalysts have generated tremendous
interest in the last decade because they are so much cheaper than the platinum-
or palladium-based materials currently used," says Price.
"However, even though the copper zeolites have shown some very positive
properties, stability has been a deal breaker up to now," he says.
Zeolites so far have tended to break down under the high temperatures of the
exhaust gas and their ability to promote the catalytic reaction declines.
The copper zeolite catalysts developed up to now lose most of their activity
well before a vehicle has reached 100,000 miles of usage. Under U.S. federal
mandates, emission systems should operate correctly for 120,000 miles.
GM has made some important discoveries in the area of stability and Tulsa University
will help evaluate and improve the zeolites for possible applications.
Price is preparing zeolites and investigating various methods for loading the
zeolites with copper. GM’s R & D centre is testing the materials for catalytic
activity and for structural integrity.
Both GM and the National Science Foundation are providing funding for the project.
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