Mitchell Young Christina Harris Chemistry 151 Research Paper 2 April 2014 Catalytic Converters There are many parts that make up a car, and many of them are taken for granted. One of these is a catalytic converter. They take poisonous gases that would harm the environment and humans, and convert them into non-toxic gases. The catalytic converter was invented in the mid 20 th century, put into production about 20 years later, and are now required on all cars sold in the United States and other countries. In the early 1950s reports on the smog conditions were published and one individual, Eugene Houdry took note and decided something needed to be done to reduce the smog amount. Houdry was a French mechanical engineer who specialized in catalytic oil refining. He began researching how to create a catalytic converter for gasoline engines with “Cat” style exhaust systems, and then later for
Transcript
Mitchell Young
Christina Harris
Chemistry 151 Research Paper
2 April 2014
Catalytic Converters
There are many parts that make up a car, and many of
them are taken for granted. One of these is a catalytic
converter. They take poisonous gases that would harm the
environment and humans, and convert them into non-toxic
gases. The catalytic converter was invented in the mid 20th
century, put into production about 20 years later, and are
now required on all cars sold in the United States and other
countries.
In the early 1950s reports on the smog conditions were
published and one individual, Eugene Houdry took note and
decided something needed to be done to reduce the smog
amount. Houdry was a French mechanical engineer who
specialized in catalytic oil refining. He began researching
how to create a catalytic converter for gasoline engines
with “Cat” style exhaust systems, and then later for
forklifts. One of the problems that faced widespread
popularity of catalytic converters was the use of leaded
gasoline. Leaded gasoline forms a layer of lead on the
surface of the converter, which makes it unable to convert
the toxic gases into non-toxic gases, making it useless. It
wasn’t until 1973 that a team of engineers from the
Engelhard Corporation perfected the design of the catalytic
converter and put it into production. These converters were
made mandatory in all vehicles in the United States in 1992.
Catalytic converters are positioned between the headers
and mufflers of an exhaust system in a vehicle, as shown in
Figure 1:
Figure 1
The raw exhaust gases come out the engine, into the headers
and into the catalytic converter. The poisonous exhaust
gases, which are a result of incomplete combustion of
gasoline, are converted to nonpoisonous gases, the exhaust
leaves the catalytic converter, and flows out of the
tailpipe and into the exterior environment.
There are three metals used for catalyzing reactions in
the substrates in catalytic converters: platinum (Pt),
palladium (Pd), and rhodium (Rh). The Platinum, palladium,
and rhodium allow the reactions HC H20 (hydrocarbon to
water), CO CO2, (carbon monoxide to carbon dioxide), and
NOx N2 (nitrogen oxides to nitrogen) to take place.
Platinum is an excellent oxidation catalyst and is ideal for
catalytic converters because of its resistance to poisonous
substances that are often found in engine exhaust such as
sulfur, lead, and phosphorus. The drawbacks of platinum are
its inefficiency to catalyze NOx (nitrogen oxides),
sensitivity to high temperatures, and higher costs than
palladium. Palladium is excellent at oxidizing hydrocarbons,
and decent at removing nitrogen oxides. Palladium’s
resistance to heat is a plus, but it is sensitive to
poisons, which can be problematic if used in a catalytic
converter that has dirty exhaust, meaning there are many
poisons in the exhaust. Rhodium is the best metal for
oxidizing hydrocarbons and carbon monoxide, and removing
nitrogen oxides out of the three metals. It is very
resistant to poisonous gases, and to high temperatures. The
only significant drawback to rhodium is the cost, which is
much higher than platinum or palladium. (Figure 2)
Figure 2
There are three main types of catalytic converters,
two-way catalytic converters, three-way catalytic
converters, and three-way plus catalytic converters. Two-way
catalytic converters are the least effective of the three
types at neutralizing poisonous gases. This is because the
substrate uses only platinum and palladium, but lacks
rhodium, which is the main metal used in the removal of
nitrogen oxides. (Figure 3)
Figure 3
Conversion of hydrocarbons and carbon monoxide to water and
carbon dioxide was efficient, but nitrogen oxides were still
present in the exhaust after the catalytic converter that
are harmful. Because of the intensity of these reactions,
there is a large amount of heat generated in the converter,
so much so that heat shields are required around the
converter, and the temperature of the exhaust exiting the
converter is greater than the temperature of the exhaust
when it enters the converter. Because of the ineffectiveness
of converting nitrogen oxides to nitrogen, two-way catalytic
converters were phased out and three-way plus catalytic
converters were introduced in the mid 1970’s.
Three-way plus catalytic converters fixed the issue of
nitrogen oxide emissions, but raised new problems. In three-
way catalytic converters there are two substrates. The first
is covered with rhodium, which fixes the problem that two-
way catalytic converters have of too much nitrogen oxides in
the emissions by converting the nitrogen oxides into
nitrogen and oxygen gases. The second substrate is coated
with platinum and palladium that catalyze hydrocarbons and
carbon monoxide into water and carbon dioxide, just like the
two-way converter does. In-between the first and second
substrate there is an air tube that allows oxygen gas (O2)
to enter the converter. This oxygen gas helps the carbon
monoxide and hydrocarbons to react in the second substrate.
(Figure 4)
Figure 4
Unfortunately because it required an air tube to allow
oxygen in, the three-way plus catalytic converter is
inefficient. Under high loads, or when there is a lean
mixture (high oxygen content in the fuel) the oxygen
concentration in the converter becomes too high, causing the
second substrate to be saturated with too many oxygen
molecules, which doesn’t allow the hydrocarbons and carbon
monoxide to be converted into water and carbon dioxide. This
inefficiency caused the development of an improved design
known as the three-way catalytic converter.
Three-way catalytic converters were implemented in
vehicles around the world since 1981. They are still in use
today and are required on all new gasoline powered vehicles
sold in the United States. Three-way catalytic converters
are, by far, the most complex of the three types of
catalytic converters. The mechanical side of three-way
converters is fairly simple, using rhodium on the first
substrate to remove nitrogen oxides, and platinum and
palladium on the second substrates to eliminate hydrocarbons
and carbon monoxide. (Figure 5) For optimal reduction of
harmful gases, oxygen sensors are in the exhaust pipe after
the catalytic converter, and depending on what is needed,
the fuel mixture is adjusted for optimal oxygen levels.
Oxygen is also stored in the catalytic converter, and can be
released when necessary. Current vehicles have the sensors
connected to the car’s main computer system and can alert
the driver when the catalytic converter is not working at
peak efficiency.
Figure 5
Without these important pieces of machinery, the earth
would have many more pollutants than there already are. All
around, every day, catalytic converters clean up exhaust so
people can drive without harming the surrounding
environment. While one may not realize it, the basis of
everything comes down to the small atoms and molecules that
support and make up our world.
Catalytic converters remove poisonous gases in exhaust
systems. Without this converter, harmful emissions would
spew into the environment, damaging plants, animals, and our
planet as a whole. Likewise, Christ removes the poison from
our life if we allow him to. But we must make the choice
daily to allow him in our lives. Without him, thoughtless
words and harmful thoughts will fill our day.
“Your sins may be as mountains before you; but if you
humble your heart and confess your sins, trusting in the
merits of a crucified and risen Saviour, He will f orgive
and will cleanse you from all unrighteousness. God demands
of you entire conformity to His law. This law is the echo of
His voice saying to you, Holier, yes, holier still. Desire
the fullness of the grace of Christ. Let your heart be
filled with an intense longing for His righteousness, the
work of which God’s word declares is peace, and its effect
quietness and assurance forever. Your sins may be as
mountains before you; but if you humble your heart and
confess your sins, trusting in the merits of a crucified and
risen Saviour, He will forgive and will cleanse you from all
unrighteousness. God demands of you entire conformity to His
law. This law is the echo of His voice saying to you,
Holier, yes, holier still. Desire the fullness of the grace
of Christ. Let your heart be filled with an intense longing
for His righteousness, the work of which God’s word declares
is peace, and its effect quietness and assurance forever.”
