A catalyst is a substance that increases the rate of reaction by offering an alternative path that lowers the activation energy.
Two types of catalyst
- Homogeneous catalysts(shown in the brown solution)
- the catalyst is in the same phase as the reactants. They work by using their variable oxidation states to oxidise/reduce a reactant, making it more reactive.
- Heterogeneous catalysts (shown in the blue solution)
- the catalyst is in a different phase to the reactants. They are usually solids, and they provide a surface for the absorption of molecules. The molecules come together in a more advantageous arrangement.
Examples of transition metals as catalyst
- Iron - the Haber process.
- Nickel - hydrogenation of alkenes.
- Platinum - oxidation of ammonia into nitric acid.
- Vandium oxide - the Contact process.
- Manganese dioxide - decomposition of hydrogen peroxide.
- NOTE: most transition metals act as heterogeneous catalysts.(two phrases)
1. They have variable oxidation states - this allows the metal to catalyse redox reactions. They can oxidise or reduce one of the reactants to make it more reactive. The transition metal can then return to its original oxidation state by reacting with another molecule.
2. They have partially filled d-orbitals - molecules with lone pairs can coordinate bond to the metal ion to form complexes. This either increases the reactivity of the species or brings the reacting molecules closer together.
3. Absorption of molecules - their surface allows molecules to be absorbed, bringing them together in a more advantageous arrangement.
That's the end of Transition Metals as Catalyst.