By: Lance Hammell

1. CATALYSTS AND ENZYMES By: Lance Hammell

2. 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.

3. 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.

4. Specifics of Catalytic Converters • Most modern cars are equipped with three-way catalytic converters. "Three-way" 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 honeycomb-shaped ceramic structure coated with a metal catalyst, usually platinum, rhodium and/or palladium. A: Reduction Catalyst B: Oxidation Catalyst C: Honeycomb Ceramic Structure

5. 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 + O2or 2 NO2 => N2 + 2 O2

6. 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.

7. 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.

8. 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.

9. 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.

10. 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.

11. 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.

12. Bibliography How Catalytic Converters Work. howstuffworks. 19 Apr. 2005. <http://auto.howstuffworks.com/catalytic-converter1.htm>. Clark, Jim. Catalysts in the Petrochemical Industry. 19 Apr. 2005.<http://chemguide.co.uk/physical/catalysis/petrochem.htm>. Farabee, M.J. Enzymes: Organic Catalysts. 19 Apr. 2005. <http://www.emc.maricopa.edu/faculty/farabee/8108K/BioBookEnzym.html#Enzymes>.