By: Lance HammellBy: Lance Hammell

What are catalysts?What are catalysts?

Simply put, catalysts are Simply put, catalysts are substances which, when substances which, when added to a reaction, added to a reaction, increase the rate of increase the rate of reaction by providing an reaction by providing an alternate reaction alternate reaction pathway with a lower pathway with a lower activation energy (Ea).activation energy (Ea).They do this by promoting They do this by promoting proper orientation proper orientation between reacting between reacting particles.particles.In biochemistry, catalysts In biochemistry, catalysts are known as enzymes. are known as enzymes.

Catalytic ConvertersCatalytic Converters

One common application One common application for catalysts is for for catalysts is for catalytic converters.catalytic converters.

Catalytic converters are Catalytic converters are found in automobiles.found in automobiles.

Their role is to reduce to Their role is to reduce to emissions of harmful emissions of harmful gases (CO, VOC’s, NOx) gases (CO, VOC’s, NOx) that are the result of the that are the result of the combustion of fuel in combustion of fuel in vehicle engines.vehicle engines.

Specifics of Catalytic ConvertersSpecifics of Catalytic Converters

Most modern cars are Most modern cars are equipped with equipped with three-way three-way catalytic converterscatalytic converters. "Three-. "Three-way" refers to the three way" refers to the three regulated emissions it helps to regulated emissions it helps to reduce -- carbon monoxide, reduce -- carbon monoxide, VOCs and NOx molecules. VOCs and NOx molecules. The converter uses two The converter uses two different types of catalysts, a different types of catalysts, a reduction catalystreduction catalyst and an and an oxidization catalystoxidization catalyst. Both . Both types consist of a honeycomb-types consist of a honeycomb-shaped ceramic structure shaped ceramic structure coated with a metal catalyst, coated with a metal catalyst, usually platinum, rhodium usually platinum, rhodium and/or palladium. and/or palladium.

A: Reduction CatalystB: Oxidation CatalystC: Honeycomb Ceramic Structure

Step 1: The Reduction CatalystStep 1: The Reduction Catalyst

The The reduction catalystreduction catalyst is the first stage of the is the first stage of the catalytic converter. catalytic converter. It uses platinum and rhodium to help reduce the It uses platinum and rhodium to help reduce the NOx emissions. When an NO or NONOx emissions. When an NO or NO22 molecule molecule contacts the catalyst, the catalyst rips the nitrogen contacts the catalyst, the catalyst rips the nitrogen atom out of the molecule and holds on to it, atom out of the molecule and holds on to it, freeing the oxygen in the form of Ofreeing the oxygen in the form of O22. . The nitrogen atoms bond with other nitrogen The nitrogen atoms bond with other nitrogen atoms that are also stuck to the catalyst, forming atoms that are also stuck to the catalyst, forming NN22..The equation for this is as follows:The equation for this is as follows:

2 NO => N2 NO => N22 + O + O22 oror 2 NO 2 NO22 => N => N22 + 2 O + 2 O22

Step 2: The Oxidization CatalystStep 2: The Oxidization Catalyst

The The oxidation catalystoxidation catalyst is the second stage of the is the second stage of the catalytic converter. catalytic converter. It reduces the unburned hydrocarbons and carbon It reduces the unburned hydrocarbons and carbon monoxide by burning (oxidizing) them over a platinum monoxide by burning (oxidizing) them over a platinum and palladium catalyst. and palladium catalyst. This catalyst aids the reaction of the CO and This catalyst aids the reaction of the CO and hydrocarbons with the remaining oxygen in the exhaust hydrocarbons with the remaining oxygen in the exhaust gas. gas. The equation for this process is as follows:The equation for this process is as follows:

2 CO + O2 CO + O22 => 2 CO => 2 CO22 Once this process is complete, most of the harmful Once this process is complete, most of the harmful substances have been broken down into harmless ones substances have been broken down into harmless ones such as Nsuch as N22, O, O22, and CO, and CO22..

Catalysts in IndustryCatalysts in Industry

Of course, reducing vehicle Of course, reducing vehicle emissions is not the only area emissions is not the only area in which catalysts can prove in which catalysts can prove useful. The petrochemical useful. The petrochemical industry also makes great use industry also makes great use of them in various processes. of them in various processes. One of these processes, called One of these processes, called catalytic cracking, is detailed catalytic cracking, is detailed below. Catalytic cracking is the below. Catalytic cracking is the name given to the breaking up name given to the breaking up of large hydrocarbon of large hydrocarbon molecules into smaller, more molecules into smaller, more useful pieces.useful pieces.

Catalytic Cracking: Part 1:Catalytic Cracking: Part 1:

Hydrocarbons are the result of the fractional distillation of gas oil Hydrocarbons are the result of the fractional distillation of gas oil from crude oil (petroleum). These fractions are obtained from the from crude oil (petroleum). These fractions are obtained from the distillation process as liquids, but are re-vaporised before cracking.distillation process as liquids, but are re-vaporised before cracking.The hydrocarbons are mixed with a very fine catalyst powder. These The hydrocarbons are mixed with a very fine catalyst powder. These days, the catalysts are zeolites (complex alumniosilicates).days, the catalysts are zeolites (complex alumniosilicates).In the past, the catalyst used was aluminum oxide and silicon In the past, the catalyst used was aluminum oxide and silicon dioxide, however, these are much less efficient than the modern dioxide, however, these are much less efficient than the modern zeolite.zeolite.The whole mixture (hydrocarbons and zeolites) is blown through a The whole mixture (hydrocarbons and zeolites) is blown through a reaction chamber at a temperature of about 500 C. The catalyst is reaction chamber at a temperature of about 500 C. The catalyst is recovered afterwards, and the cracked mixture is further separated recovered afterwards, and the cracked mixture is further separated by cooling and fractional distillation.by cooling and fractional distillation.

Catalytic Cracking: Part 2:Catalytic Cracking: Part 2:

There isn’t any single unique reaction happening during There isn’t any single unique reaction happening during this process. The hydrocarbon molecules are broken up this process. The hydrocarbon molecules are broken up in a fairly random way to produce mixtures of smaller in a fairly random way to produce mixtures of smaller hydrocarbons, some of which have carbon double hydrocarbons, some of which have carbon double bonds. However, one possible reaction might be:bonds. However, one possible reaction might be:

CC1515HH32 32 2 C 2 C22HH4 4 + C+ C33HH6 6 + C+ C66HH1818

zeolitezeoliteThis is only one way in which this particular molecule This is only one way in which this particular molecule might break up. This process is important because Cmight break up. This process is important because C22HH4 4

(ethene) and C(ethene) and C33HH8 8 (propene) are important materials for (propene) are important materials for making plastics or producing other organic chemicals. making plastics or producing other organic chemicals. The octane (CThe octane (C88HH1818) is one of the molecules found in ) is one of the molecules found in gasoline.gasoline.

Enzymes: Organic Catalysts:Enzymes: Organic Catalysts:

An enzyme is essentially a An enzyme is essentially a catalyst that is found in living catalyst that is found in living things.things.Enzymes are proteins.Enzymes are proteins.They are specific – their shape They are specific – their shape determines which substrate determines which substrate they work with.they work with.Enzymes bind temporarily to Enzymes bind temporarily to one or more of the reactants of one or more of the reactants of the reaction they catalyze. In the reaction they catalyze. In doing so, they lower the doing so, they lower the amount of amount of activation energyactivation energy needed by promoting the needed by promoting the proper orientation between proper orientation between particles and thus speed up particles and thus speed up the reaction. the reaction.

Enzymes: Cont’d:Enzymes: Cont’d:

As we well remember, the function of enzymes and catalysts is to As we well remember, the function of enzymes and catalysts is to speed up a reaction, and they do this by promoting proper speed up a reaction, and they do this by promoting proper orientation between reacting particles.orientation between reacting particles.Thus the function of enzymes and how they work becomes Thus the function of enzymes and how they work becomes immediately clear when considered in the context of the role of immediately clear when considered in the context of the role of catalysts.catalysts.An example of an enzyme with equation would be carbonic An example of an enzyme with equation would be carbonic anhydrase, which is found in red blood cells. During the rxn COanhydrase, which is found in red blood cells. During the rxn CO2 2 + + HH22O O H H22COCO33, it enables red blood cells to transport CO, it enables red blood cells to transport CO22 from the from the tissue to the lungs, where it can be expelled.tissue to the lungs, where it can be expelled.Obviously, enzymes are extremely important. By allowing rapid Obviously, enzymes are extremely important. By allowing rapid processing of COprocessing of CO22 (1,000,000 molecules of CO (1,000,000 molecules of CO22/sec.), they help to /sec.), they help to ensure that we remain alive!ensure that we remain alive!This is only one example of the importance of enzymes – there are This is only one example of the importance of enzymes – there are thousands or even millions of these substances at work in all living thousands or even millions of these substances at work in all living things.things.

BibliographyBibliography

How Catalytic Converters WorkHow Catalytic Converters Work. howstuffworks. 19 Apr. . howstuffworks. 19 Apr. 2005. <http://auto.howstuffworks.com/catalytic-2005. <http://auto.howstuffworks.com/catalytic-converter1.htm>.converter1.htm>.

Clark, Jim. Catalysts in the Petrochemical Industry. 19 Apr. Clark, Jim. Catalysts in the Petrochemical Industry. 19 Apr. 2005.<http://chemguide.co.uk/physical/catalysis/petroch2005.<http://chemguide.co.uk/physical/catalysis/petrochem.htm>.em.htm>.

Farabee, M.J. Enzymes: Organic Catalysts. 19 Apr. 2005. Farabee, M.J. Enzymes: Organic Catalysts. 19 Apr. 2005. <http://www.emc.maricopa.edu/faculty/farabee/8108K/Bi<http://www.emc.maricopa.edu/faculty/farabee/8108K/BioBookEnzym.html#Enzymes>.oBookEnzym.html#Enzymes>.

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