A promoter in catalysis is a substance that enhances the efficiency or effectiveness of a catalyst without itself being a primary catalyst. It doesn’t directly cause the reaction but improves the catalyst’s performance in several ways.
1. Functions of a Promoter
- Increase Activity
- Makes the catalyst more reactive.
- Helps reactants adsorb better or speeds up intermediate reactions.
- Enhance Selectivity
- Helps the catalyst produce more of the desired product and fewer byproducts.
- Improve Stability
- Prevents the catalyst from degrading, sintering, or getting poisoned over time.
- Modify Surface Properties
- Changes the surface structure or electronic properties of the catalyst to make it more effective.
2. Examples of Promoters
- Iron catalyst in Haber process:
- Promoters: K₂O, Al₂O₃, CaO
- Function: Increase activity and stability of iron for ammonia synthesis.
- Vanadium pentoxide (V₂O₅) in the Contact process:
- Promoter: K₂SO₄
- Function: Enhances the activity of V₂O₅ for oxidizing SO₂ to SO₃.
3. Key Point
- A promoter is not a catalyst by itself.
- It only improves the performance or durability of the main catalyst.
In short: Promoters help catalysts work better—they boost activity, selectivity, and longevity without directly causing the reaction.