Catalysts and Altering Octane Numbers - Chemical Ideas 10.5
Catalysts
A catalyst is a substance or compound which is used in a reaction to help lower the activation energy needed for the reactants to react. This therefore allows the reaction to take place quicker. A catalyst is also unharmed in the reaction and can be used again after the reaction has finished. This process is called catalysis. There are two types of catalysis;
Heterogeneous catalysts work when the reactants have different physical states (eg. A solid and a liquid)
Homogeneous catalysts work when the reactants have the same physical states (eg. Two liquids)
An example of a catalyst can be found in cars. Catalytic converters are used in cars to help remove poisonous gases. Catalytic converters also only work when the temperature is high and therefore don’t work at the start of a journey or in the cold weather. Rhodium or platinum are used as a heterogeneous catalyst in the catalytic converter. The following equation is an example of one that occurs in a catalytic converter.
2NO (g) + 2CO (g) ----------> N2 (g) + 2CO2 (g)
Process of a Catalyst
1) Reactants are adsorbed onto the surface of the catalyst
2) Bonds between the atoms in the reactants break
3) New bonds and compounds are formed
4) The products diffuse away
Catalysts and Petrol Components
There are three processes performed at an oil refinery which involve catalysts. These processes mean the fuel created can have a higher octane number and therefore have less tendency to auto-ignite. The three reactions are cracking, reforming and isomerisation. These can be seen below.
Cracking
- A shorter, sometimes branched, alkane is formed alongside an alkene. This gives the hydrocarbons a higher octane number.
- A zeolite is used as the catalyst.
Reforming
- Long alkanes are converted to cycloalkanes and hydrogen.
- Cycloalkanes are then converted into arenes and hydrogen.
- Arenes have a higher octane number than cycloalkanes, and cycloalkanes have a higher octane number than alkanes.
- Platinum is used as the catalyst.
Isomerisation
In developing fuels isomerisation and isomers was covered. This is a way of re-drawing compounds which have the same molecular structure but different structual fromula.
A branched molecule has a higher octane number than a straight chain alkanes. One example is pentane which has a octane number of 62, which is converted into 2-methylbutane which has an octane number of 93. Platinum is used as the catalyst for isomerisation.
- Long alkanes are converted to cycloalkanes and hydrogen.
- Cycloalkanes are then converted into arenes and hydrogen.
- Arenes have a higher octane number than cycloalkanes, and cycloalkanes have a higher octane number than alkanes.
- Platinum is used as the catalyst.
Isomerisation
In developing fuels isomerisation and isomers was covered. This is a way of re-drawing compounds which have the same molecular structure but different structual fromula.
A branched molecule has a higher octane number than a straight chain alkanes. One example is pentane which has a octane number of 62, which is converted into 2-methylbutane which has an octane number of 93. Platinum is used as the catalyst for isomerisation.