Why transition metals are useful catalysts
Transition metals and their compounds are widely used as catalysts. A catalyst increases the rate of a reaction by providing an alternative reaction pathway of lower activation energy and is regenerated overall.
An important feature of transition-metal catalysis is the ability of the metal to form ions in different oxidation states. The metal can accept or donate electrons during intermediate steps and then return to its original oxidation state.
| Type | Relationship to reactants | Where the reaction occurs |
|---|---|---|
| Heterogeneous | Catalyst and reactants are in different phases. | At active sites on the catalyst surface. |
| Homogeneous | Catalyst and reactants are in the same phase. | Through intermediate species in the reaction mixture. |
Variable oxidation states
Changing between oxidation states allows a transition-metal catalyst to take part in one reaction step and then be regenerated in another. This creates an alternative route between the same overall reactants and products.
Industrial catalysts
- catalyses the Contact process.
- Iron catalyses the Haber process.
Ionic catalysts
- catalyses the reaction of iodide with peroxodisulfate.
- autocatalyses the manganate(VII)–ethanedioate reaction.
Exam Tip: When explaining why variable oxidation states are useful in catalysis, show that the catalyst changes oxidation state in one step and returns to its original oxidation state in a later step.