1.9.4Physical Chemistry
Catalysts in Industry — Edexcel AS Chemistry Revision Notes & Topical Questions
5 min read 5 parts Lesson 41 of 42
Part 1 of 5Types of Catalyst
Heterogeneous
- Catalyst in a different phase from the reactants, usually a solid with gaseous or liquid reactants.
Homogeneous
- Catalyst in the same phase as the reactants, such as aqueous acid catalysing a reaction in solution.
Surface action
- Heterogeneous catalysts work through reactant molecules adsorbing onto the surface, reacting and then leaving.
Separation
- Heterogeneous catalysts are easy to separate from products, which is a major advantage in industry.
Active sites
- Reactants adsorb onto active sites on the surface, so a finely divided or supported catalyst gives a larger working area.
Part 2 of 5Industrial Examples
Industrial Examples
Haber process
- Iron catalyses the reaction N₂(g) + 3H₂(g) ⇌ 2NH₃(g) at a moderate temperature of about 450 °C.
Catalytic converters
- Platinum, palladium or rhodium on a honeycomb support convert 2CO + 2NO → 2CO₂ + N₂.
Hydrogenation of alkenes
- Nickel catalyses the addition of hydrogen to double bonds, as in manufacture of margarine.
Choice of metal
- Transition metals are widely used because they can adsorb molecules and change oxidation state.
Enzymes
- Biological catalysts called enzymes work in the same way, lowering activation energy for reactions in living organisms.
| Process | Catalyst | Phase |
|---|---|---|
| Haber process | Iron | Solid with gaseous reactants |
| Catalytic converter | Pt, Pd, Rh | Solid with gaseous reactants |
| Alkene hydrogenation | Nickel | Solid with gas and liquid |
Part 3 of 5Why Industry Uses Catalysts
1
A catalyst lowers the activation energy, allowing reactions to proceed at lower temperature.
2
Lower temperatures reduce energy costs and the demand for fuel.
3
Using less fuel lowers carbon dioxide emissions and helps sustainability.
4
The catalyst is not used up, so it can be reused many times.
5
Catalysts can improve selectivity so that more of the desired product forms and less waste is made.
Part 4 of 5Limitations and Care
Catalyst poisoning
- Impurities such as sulfur compounds can bind to the surface and stop the catalyst working.
Cost
- Metals such as platinum and rhodium are expensive, so recovery and recycling are important.
Toxicity
- Some catalysts and their waste can be toxic, so safe disposal is needed.
No change in equilibrium
- A catalyst speeds up forward and reverse reactions equally, so equilibrium yield is the same.
Part 5 of 5Exam Checklist & Tips
1.9.4 – Key Points for the Exam
- Heterogeneous catalyst Catalyst in a different phase from the reactants.
- Homogeneous catalyst Catalyst in the same phase as the reactants.
- Adsorption Molecules attaching to the surface of a solid.
- Catalyst poison A substance that blocks active sites and reduces catalyst activity.
Common Mistakes
- Saying catalysts are used up in a reaction.
- Claiming a catalyst changes the equilibrium position or the enthalpy change.
- Forgetting to state the phases when classifying a catalyst as homogeneous or heterogeneous.
- Writing that catalysts increase the energy of the molecules.
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