1. Something that causes an important event to happen.
2. (Chemistry) A substance that initiates or accelerates a chemical reaction without itself being affected; SYN. accelerator.
A substance that changes the speed or yield of a chemical reaction without being consumed or chemically changed by the chemical reaction
Substance that alters the speed of, or makes possible, a chemical or biochemical reaction but remains unchanged at the end of the reaction. Enzymes are natural biochemical catalysts. In practice most catalysts are used to speed up reactions. + prikaži više

1. Someone who is an active supporter and advocate; SYN. booster, plugger.
2. A substance that in very small amounts is able to increase the activity of a catalyst

Antipollution device on an automotive exhaust system.
Device fitted to the exhaust system of a motor vehicle in order to reduce toxic emissions from the engine. It converts harmful exhaust products to relatively harmless ones by passing the exhaust gases over a mixture of catalysts coated on a metal or ceramic honeycomb (a structure that increases the surface area and therefore the amount of active catalyst with which the exhaust gases will come into contact). Oxidation catalysts (small amounts of precious palladium and platinum metals) convert hydrocarbons (unburned fuel) and carbon monoxide into carbon dioxide and water, but do not affect nitrogen oxide emissions. Three-way catalysts (platinum and rhodium metals) convert nitrogen oxide gases into nitrogen and oxygen.
Over the lifetime of a vehicle, a catalytic converter can reduce hydrocarbon emissions by 87%, carbon monoxide emissions by 85%, and nitrogen oxide emissions by 62%, but will cause a slight increase in the amount of carbon dioxide emitted. Catalytic converters are standard in the US, where a 90% reduction in pollution from automobiles was achieved without loss of engine performance or fuel economy. Only 10% of automobiles in Britain had catalytic converters 1993.
Catalytic converters are destroyed by emissions from leaded gasoline and work best at a temperature of 300şC. The benefits of catalytic converters are offset by any increase in the number of automobiles in use. + prikaži više

A chemical reactor for converting oils with high boiling points into fuels with lower boiling points in the presence of a catalyst; SYN. cat cracker.
The unit in a petroleum refinery in which cracking is carried out in the presence of a catalyst