katalysi

Katalysi, also called catalysis, is the acceleration of a chemical reaction by a substance—the catalyst—that is not consumed in the overall process. The catalyst provides an alternative reaction pathway with a lower activation energy, allowing more reactant molecules to react in a given time. After the reaction, the catalyst is regenerated and can catalyze additional cycles.

Catalysis can be categorized by the phase relationship between catalyst and reactants. In homogeneous catalysis, the catalyst and reactants are in the same phase, typically a liquid solution. In heterogeneous catalysis, the catalyst is in a different phase, usually a solid, and reactions occur at the catalyst surface. Biocatalysis uses biological catalysts, most often enzymes, offering high specificity and operate under mild conditions. Other notable types include photocatalysis, where light drives the reaction, and electrocat­alysis, where electrical input influences the rate.

Mechanisms vary but often involve adsorption of reactants onto active sites, formation of reaction intermediates, and desorption of products. Catalysts work by enhancing rate without altering the overall stoichiometry, and are not consumed in the reaction. They may also influence selectivity, steering products toward a preferred outcome.

Applications are widespread. In industry, catalysts enable ammonia synthesis (Haber-Bosch), sulfuric acid production, and catalytic cracking in petroleum refining. Automotive catalytic converters use platinum-group metals to reduce harmful emissions. In polymerization and organic synthesis, catalysts improve efficiency and enable complex transformations. Biocatalysis underpins many pharmaceutical syntheses and green chemistry initiatives.

Key considerations include catalyst activity, selectivity, stability, and resistance to poisoning. Common metrics are turnover number and turnover frequency, which quantify how many reaction cycles a catalyst can perform over time. The field continues to explore new materials, sustainable processes, and environmentally friendly catalysts.