Adapted from powerpoint created by Lance Hammell

Chemical Reaction 13.1 Reactant Bonds Broken, Product Bonds Made NO 2 (g) + CO (g) -> NO (g) + CO 2 (g) N OO O O OO C C + + N Lisa R. Arnold South Georgia College

Molecular Collision Theory Reactants must collide with a)correct orientation b)enough energy, E a O C O O N OO O C N Incorrect Orientation Correct Orientation Lisa R. Arnold South Georgia College

4 Reaction path for conversion of A + B into AB Abdul-Rahman Al-Betar

A + B C + D Exothermic Reaction Endothermic Reaction The activation energy (E a ) is the minimum amount of energy required to initiate a chemical reaction Lisa R. Arnold South Georgia College

Activation Energy....is energy needed so there is enough energy to break reactant bonds...is the energy needed to get molecules in the correct orientation...is the energy needed to reach the transition state or activated complex Lisa R. Arnold South Georgia College

7 Activation Energy The Activation Energy (Ea) determines how fast a reaction occurs, the higher Activation barrier, the slower the reaction rate. The lower the Activation barrier, the faster the reaction Abdul-Rahman Al-Betar

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.

9 Catalyst lowers the activation energy for both forward and reverse reactions. Activation Energy Abdul-Rahman Al-Betar

10 Activation Energy This means, the catalyst changes the reaction path by lowering its activation energy and consequently the catalyst increases the rate of reaction. Abdul-Rahman Al-Betar

Why do we need catalysts? CEBC video CEBC video

12 Adsorption and Absorption H H H H H H H HH H H H H H H H HH H H H H H H H H H H H H H H H H H H H 2 absorption  palladium hydride H 2 adsorption on palladium Surface process bulk process Abdul-Rahman Al-Betar

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. "Three-way" refers to the three regulated emissions it helps to reduce -- carbon monoxide, VOCs and NOx molecules. A: Reduction Catalyst B: Oxidation Catalyst C: Honeycomb Ceramic Structure The converter uses two different types of catalysts, Both types consist of a honeycomb-shaped ceramic structure coated with a metal catalyst, usually platinum, rhodium and/or palladium.

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 NO 2 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 O 2. The nitrogen atoms bond with other nitrogen atoms that are also stuck to the catalyst, forming N 2. The equation for this is as follows: 2 NO => N 2 + O 2 or 2 NO 2 => N O 2

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 + O 2 => 2 CO 2

Once this process is complete, most of the harmful substances have been broken down into harmless ones such as N 2, O 2, and CO 2. Catalytic Converter Summary Catalytic Converter Summary

Applications of Catalysts Fuel Cells Fuel Cells