Catalysts

What does a catalyst do and how does it do this?

A catalyst increases the rate of reaction by providing an alternative reaction pathway of lower activation energy (E_c)

• This results in more molecules having energy which exceeds the E_a

Describe the use of a catalyst

• Is not used up in a chemical reaction (doesn’t appear in reaction equation)

• May react to form an intermediate or may provide a surface on which a reaction can take place

• At the end of the reaction the catalyst is generated

Name the 2 types of catalyst

• Homogeneous catalyst

• Heterogeneous catalyst

Describe a homogeneous catalyst

• Homogeneous catalyst - a catalyst which has the same physical state as the reactants

  • It reacts with reactants to form an intermediate, which then breaks down to give the product and regenerates the catalyst

Give 2 examples of a homogeneous catalyst

• Formation of esters by reacting alcohol with carboxylic acid (liquid sulfuric acid catalyst)

• Ozone depletion (Cl• radicals as catalyst)

Describe a heterogeneous catalyst

• Heterogeneous catalyst - catalyst with a different physical state from the reactants

  • Usually solids in contact with gaseous reactions or reactants in solution

    • Reactant molecules are adsorbed (weakly bonded) onto the surface of the catalyst, where the reaction takes place

    • After the reaction, the product molecules leave the surface of the catalyst by desorption

Define adsorption

Adsorption - process that occurs when a gas, liquid or solute is held on the surface of a solid or liquid

Explain the process that takes place in catalytic converters

1. Adsorption of NO and CO to the catalyst surface

2. Weakens the bonds between the reactant molecules

3. A chemical reaction takes place and new bonds form - CO₂ and N₂ are formed

4. Desorption of CO₂ and N₂ from the catalyst

Give 3 sustainable and economic benefits of catalysts

Catalysts help to lower the energy demands of processes, leading to:

• Reduced costs - less fossil fuel burned to generate energy required

• Lower CO₂ emissions - helps the environment

• High atom economies and fewer pollutants which is required by industry