Transcript CATALYSTS AND THEIR APPLICATION IN TRANSPORTATION

By: Lance Hammell
What are catalysts?
Simply put, catalysts are
substances which, when
added to a reaction,
increase the rate of
reaction by providing an
alternate reaction
pathway with a lower
activation energy (Ea).
They do this by promoting
proper orientation
between reacting
particles.
In biochemistry, catalysts
are known as enzymes.
Catalytic Converters
One common application
for catalysts is for
catalytic converters.
Catalytic converters are
found in automobiles.
Their role is to reduce to
emissions of harmful
gases (CO, VOC’s, NOx)
that are the result of the
combustion of fuel in
vehicle engines.
Specifics of Catalytic Converters
Most modern cars are
equipped with three-way
catalytic converters. "Threeway" refers to the three
regulated emissions it helps to
reduce -- carbon monoxide,
VOCs and NOx molecules.
The converter uses two
different types of catalysts, a
reduction catalyst and an
oxidization catalyst. Both
types consist of a honeycombshaped ceramic structure
coated with a metal catalyst,
usually platinum, rhodium
and/or palladium.
A: Reduction Catalyst
B: Oxidation Catalyst
C: Honeycomb Ceramic Structure
Step 1: The Reduction Catalyst
The reduction catalyst is the first stage of the
catalytic converter.
It uses platinum and rhodium to help reduce the
NOx emissions. When an NO or NO2 molecule
contacts the catalyst, the catalyst rips the
nitrogen atom out of the molecule and holds on
to it, freeing the oxygen in the form of O2.
The nitrogen atoms bond with other nitrogen
atoms that are also stuck to the catalyst, forming
N2.
The equation for this is as follows:
2 NO => N2 + O2 or 2 NO2 => N2 + 2 O2
Step 2: The Oxidization Catalyst
The oxidation catalyst is the second stage of the
catalytic converter.
It reduces the unburned hydrocarbons and carbon
monoxide by burning (oxidizing) them over a platinum
and palladium catalyst.
This catalyst aids the reaction of the CO and
hydrocarbons with the remaining oxygen in the exhaust
gas.
The equation for this process is as follows:
2 CO + O2 => 2 CO2
Once this process is complete, most of the harmful
substances have been broken down into harmless ones
such as N2, O2, and CO2.
Catalysts in Industry
Of course, reducing vehicle
emissions is not the only area
in which catalysts can prove
useful. The petrochemical
industry also makes great use
of them in various processes.
One of these processes, called
catalytic cracking, is detailed
below. Catalytic cracking is the
name given to the breaking up
of large hydrocarbon
molecules into smaller, more
useful pieces.
Catalytic Cracking: Part 1:
Hydrocarbons are the result of the fractional distillation of gas oil
from crude oil (petroleum). These fractions are obtained from the
distillation process as liquids, but are re-vaporised before cracking.
The hydrocarbons are mixed with a very fine catalyst powder. These
days, the catalysts are zeolites (complex alumniosilicates).
In the past, the catalyst used was aluminum oxide and silicon
dioxide, however, these are much less efficient than the modern
zeolite.
The whole mixture (hydrocarbons and zeolites) is blown through a
reaction chamber at a temperature of about 500 C. The catalyst is
recovered afterwards, and the cracked mixture is further separated
by cooling and fractional distillation.
Catalytic Cracking: Part 2:
There isn’t any single unique reaction happening during
this process. The hydrocarbon molecules are broken up
in a fairly random way to produce mixtures of smaller
hydrocarbons, some of which have carbon double
bonds. However, one possible reaction might be:
C15H32  2 C2H4 + C3H6 + C6H18
zeolite
This is only one way in which this particular molecule
might break up. This process is important because C2H4
(ethene) and C3H8 (propene) are important materials for
making plastics or producing other organic chemicals.
The octane (C8H18) is one of the molecules found in
gasoline.
Enzymes: Organic Catalysts:
An enzyme is essentially a
catalyst that is found in living
things.
Enzymes are proteins.
They are specific – their shape
determines which substrate
they work with.
Enzymes bind temporarily to
one or more of the reactants of
the reaction they catalyze. In
doing so, they lower the
amount of activation energy
needed by promoting the
proper orientation between
particles and thus speed up
the reaction.
Enzymes: Cont’d:
As we well remember, the function of enzymes and catalysts is to
speed up a reaction, and they do this by promoting proper
orientation between reacting particles.
Thus the function of enzymes and how they work becomes
immediately clear when considered in the context of the role of
catalysts.
An example of an enzyme with equation would be carbonic
anhydrase, which is found in red blood cells. During the rxn CO2 +
H2O  H2CO3, it enables red blood cells to transport CO2 from the
tissue to the lungs, where it can be expelled.
Obviously, enzymes are extremely important. By allowing rapid
processing of CO2 (1,000,000 molecules of CO2/sec.), they help to
ensure that we remain alive!
This is only one example of the importance of enzymes – there are
thousands or even millions of these substances at work in all living
things.
Bibliography
How Catalytic Converters Work. howstuffworks. 19 Apr.
2005. <http://auto.howstuffworks.com/catalyticconverter1.htm>.
Clark, Jim. Catalysts in the Petrochemical Industry. 19 Apr.
2005.<http://chemguide.co.uk/physical/catalysis/petroch
em.htm>.
Farabee, M.J. Enzymes: Organic Catalysts. 19 Apr. 2005.
<http://www.emc.maricopa.edu/faculty/farabee/8108K/Bi
oBookEnzym.html#Enzymes>.
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