catalise

Catalyse, or catalysis in American spelling, is the process by which a substance called a catalyst increases the rate of a chemical reaction without being consumed in the overall process. A catalyst provides an alternative reaction pathway with a lower activation energy, allowing more reactant molecules to surmount the energy barrier at a given temperature. The catalyst is not consumed and is recovered unchanged at the end of the reaction, though it may be temporarily modified or occupied by intermediates.

Catalysts are classified by phase: homogeneous catalysts operate in the same phase as the reactants; heterogeneous catalysts are in a different phase, commonly a solid catalyst with gas or liquid reactants. Enzymes are biological catalysts that operate under mild conditions and with high specificity. Catalysis can also be based on radicals, surface chemistry, or electron transfer.

Common principles include adsorption of reactants on active sites, formation of intermediate species, and desorption of products. Catalyst performance is characterized by rate enhancement, turnover frequency, selectivity, and stability. Deactivation by fouling, sintering, poisoning by poisons, or harsh conditions is a major consideration in industrial use.

Industrial examples include the iron catalyst used in ammonia synthesis (Haber–Bosch), vanadium(V) oxide in the contact process for sulfuric acid production, or nickel catalysts for hydrogenation. Zeolites and other solid catalysts enable cracking and hydrocracking in petroleum refining. The term 'catalyse' derives from Greek kata and lysis; 'catalysis' is the noun, and 'catalyst' the substance; in British English the verb is often 'catalyse', while in American English it is 'catalyze'.