Catalysts

Understanding Catalysts

• Catalysts are substances which increase the rate of a reaction by providing an alternative reaction pathway with a lower activation energy.
• They are not consumed in the reaction, meaning they’re available for reuse.
• Catalysts are specific for certain reactions, with enzymes being biological catalysts.

Catalysts and Energy Profiles

• Catalysts lower the activation energy of a reaction - the energy needed to break the bonds in the reactants.
• This is depicted on an energy profile, where the addition of a catalyst lowers the peak of the energy ‘hill’.
• The catalyst does not affect the overall energy change (enthalpy change) for the reaction.

Catalyst Types and Their Functions

• Heterogeneous catalysts are in a different phase to the reactants. They work by providing a surface where the reactants can come together, reducing the energy needed for the reaction.
• Homogeneous catalysts are in the same phase as the reactants (usually both in solution). They work by forming an intermediate compound with the reactant, changing the pathway of the reaction.

Environmental and Economic Implications of Catalysts

• The use of catalysts can increase the rate and selectivity of reactions, reducing waste products and energy consumption.
• Developments in catalyst technology are essential for more efficient fuel production methods.
• Sometimes catalysts can become ‘poisoned’ by impurities, reducing their effectiveness.

Catalytic Converters

• Catalytic converters in vehicles contain catalysts that facilitate reactions to reduce harmful exhaust emissions.
• The catalysts typically used are platinum, palladium and rhodium.
• They facilitate reactions such as the conversion of Carbon Monoxide (CO) and Nitrogen Oxides (NOx) to less harmful gases.