Katalyysi

Katalyysi, in chemistry, is the process by which the rate of a chemical reaction is increased by a substance, the catalyst, which is not consumed in the overall reaction. The presence of a catalyst offers an alternative reaction pathway with a lower activation energy, allowing more reactant molecules to react per unit time under given conditions. Catalysts themselves are not permanently altered; they participate in reaction cycles and can be regenerated.

Catalysis can be classified by phase (homogeneous: catalyst and reactants in the same phase; heterogeneous: catalyst in a different phase; biocatalysis: enzymes as biological catalysts). Other important branches include photocatalysis and electrocatalysis, which use light or electric current to drive catalytic cycles.

There are many mechanisms, including adsorption of reactants on a catalyst surface, surface reactions, and desorption of products. Models such as Langmuir-Hinshelwood and Eley-Rideal describe how reactions occur on surfaces. Catalysts influence selectivity and efficiency, not the thermodynamic equilibrium.

Industrially important catalysts include iron for the Haber-Bosch process, vanadium(V) oxide for the contact process, and noble metals in automotive catalytic converters. In biology, enzymes are natural catalysts enabling essential processes at moderate temperatures and pH.

Applications span energy, chemicals, and environmental protection, from sustainable fuel production to pollution reduction. Challenges include catalyst deactivation, poisoning by impurities, and cost or scarcity of materials.

Historical note: the term katalyysi or catalysis was introduced in the 1830s by Jöns Jakob Berzelius, reflecting the idea of "loosening" or accelerating a reaction without being consumed.