Heterogenous Catalysts

Make good catalysts because they can change oxidation states by gaining or losing electrons within their d orbitals. This means they can transfer electrons to speed up reactions

Vanadium (V) oxide oxidises SO2 to SO3 because it can be reduced to vanadium (IV) oxide. Then oxidised back to V (V) oxide by oxygen ready to start all over again. V2O5 + SO2 –> V2O4 + SO3 V2O4 + 1/2 O2 –> V2O5

A catalyst that is in a different phase from the reactants (ie in a different physical state)

eg in Haber Process gases are passed over a solid iron catalyst. The reaction happens on active sites located on the surface of the heterogenous catalyst. So increasing the surface area of the catalyst increases the number of molecules that can react at the same time, increasing the rate of reaction

Often used to make the area of the catalyst as large as possible. They help to minimise the cost of the reaction, because only a small coating of a catalyst is needed to provide a large surface area

N2 + 3H2 –> 2NH3 Ammonia

SO2 + 1/2 O2 –> SO3. (the SO3 reacts with water) to make Sulfuric Acid

Heterogenous catalysts often work by adsorbing reactants onto active sites located on their surfaces. Impurities in the reaction mixture may also bind to the catalyst’s surface and block reactants from being adsorbed. Catalyst poisoning

Reduces the surface area of the catalyst available to the reactants, slowing down the reaction. Catalyst poisoning increases the cost of a chemical process because less product can be made in a certain time or with a certain amount of energy. The catalyst may even need replacing or regenerating costing money

The hydrogen in the haber process is produced from methane. The methane is obtained from natural gas, which contains impurities, including sulfur compounds. Any sulfur that is not removed is adsorbed onto the iron, forming iron sulphide, and stopping the iron from catalysing the reaction efficiently