catalysator

A catalyst, or catalysator, is a substance that increases the rate of a chemical reaction without itself undergoing permanent chemical change. By providing an alternative reaction pathway with a lower activation energy, a catalyst speeds up the reaction but is not consumed in the overall process. The effect is to shift the rate, not the equilibrium position.

Catalysts are broadly classified as homogeneous (the catalyst and reactants are in the same phase), heterogeneous (different phases, usually solid catalyst with gas or liquid reactants), and biocatalysts or enzymes (protein-based catalysts that operate under mild conditions).

In industry, catalysts enable ammonia synthesis (iron catalyst at high temperature and pressure), petroleum refining, hydrocracking, and polymerization. Zeolites and solid acids enable catalytic cracking and alkylation. Automotive catalytic converters employ noble metals such as platinum, palladium, and rhodium to convert carbon monoxide, unburned hydrocarbons, and nitrogen oxides into carbon dioxide, water, and nitrogen.

Catalysts work by adsorption of reactants on surfaces, formation of reactive intermediates, and desorption of products. They can be sensitive to impurities and can be deactivated by sintering, fouling, or poisoning; regeneration or replacement may be required. Metrics used to assess performance include turnover number and turnover frequency.

The concept of catalysis was named by Berzelius in 1835. Catalysts have been used since ancient times, with major advances in heterogeneous catalysis for petrochemical processes occurring in the 20th century.