What is known as catalyst?

activation energy     (in chemistry) The minimum energy needed for a particular chemical reaction to take place.

atom     The basic unit of a chemical element. Atoms are made up of a dense nucleus that contains positively charged protons and neutrally charged neutrons. The nucleus is orbited by a cloud of negatively charged electrons.

bond     (in chemistry) A semi-permanent attachment between atoms — or groups of atoms — in a molecule. It’s formed by an attractive force between the participating atoms. Once bonded, the atoms will work as a unit. To separate the component atoms, energy must be supplied to the molecule as heat or some other type of radiation.

carbon     The chemical element having the atomic number 6. It is the physical basis of all life on Earth. Carbon exists freely as graphite and diamond. It is an important part of coal, limestone and petroleum, and is capable of self-bonding, chemically, to form an enormous number of chemically, biologically and commercially important molecules.

catalyst    A substance that helps a chemical reaction to proceed faster. Examples include enzymes and elements such as platinum and iridium.

catalytic converter     A device made of honeycomb-shaped ceramic structures that is put onto the tailpipe of a vehicle. As exhaust gases flow through it, they encounter two different types of catalysts, each able to foster a different type of chemical reaction. One or more metals, usually platinum, rhodium, palladium — and sometimes even gold — coat the inside of the system. All of the walls of the device’s honeycomb structure increase greatly the area of catalyst-covered surfaces now available to react with the exhaust. As the gases from the engine hit these metal coated surfaces, they break apart the pollutants, turning them into less harmful materials. A sensor in the converter also measures how much oxygen is in the exhaust. If it finds too much, it tells a computer to adjust the air-to-fuel ratio in the engine so that it will burn more cleanly.

chemical     A substance formed from two or more atoms that unite (become bonded together) in a fixed proportion and structure. For example, water is a chemical made of two hydrogen atoms bonded to one oxygen atom. Its chemical symbol is H2O. Chemical can also be an adjective that describes properties of materials that are the result of various reactions between different compounds.

chemical bonds     Attractive forces between atoms that are strong enough to make the linked elements function as a single unit. Some of the attractive forces are weak, some are very strong. All bonds appear to link atoms through a sharing of — or an attempt to share — electrons.

chemical reaction     A process that involves the rearrangement of the molecules or structure of a substance, as opposed to a change in physical form (as from a solid to a gas).

electricity     A flow of charge, usually from the movement of negatively charged particles, called electrons.

engine     A machine designed to convert energy into useful mechanical motion. Sometimes an engine is called a motor.

enzymes     Molecules made by living things to speed up chemical reactions.

exhaust     (in engineering) The gases and fine particles emitted — often at high speed and/or pressure — by combustion (burning) or by the heating of air. Exhaust gases are usually a form of waste.

fuel cell     A device that converts chemical energy into electrical energy. The most common fuel is hydrogen, which emits only water vapor as a byproduct.

genetic     Having to do with chromosomes, DNA and the genes contained within DNA. The field of science dealing with these biological instructions is known as genetics. People who work in this field are geneticists.

hydrogen     The lightest element in the universe. As a gas, it is colorless, odorless and highly flammable. It’s an integral part of many fuels, fats and chemicals that make up living tissues.

iridium     Discovered in 1803, its name comes from the Latin for rainbow. It’s a hard, brittle and corrosion-resistant metal in the platinum family. Slightly yellowish, the principle use for this element is as a hardener for platinum. Indeed, its melting point is more than 2,400° Celsius (4,350° Fahrenheit). The element’s atomic number is 77.

manufacturing     The making of things, usually on a large scale.

metal     Something that conducts electricity well, tends to be shiny (reflective) and malleable (meaning it can be reshaped with heat and not too much force or pressure). 

molecule     An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).

nutrient     A vitamin, mineral, fat, carbohydrate or protein that a plant, animal or other organism requires as part of its food in order to survive.

oxygen     A gas that makes up about 21 percent of the atmosphere. All animals and many microorganisms need oxygen to fuel their metabolism.

palladium     A soft, ductile, steel-white, tarnish-resistant, metallic element occurring naturally with platinum, especially in gold, nickel, and copper ores.

petroleum     A thick flammable liquid mixture of hydrocarbons. Petroleum is a fossil fuel mainly found beneath the Earth’s surface. It is the source of the chemicals used to make gasoline, lubricating oils, plastics and many other products.

plastic     Any of a series of materials that are easily deformable; or synthetic materials that have been made from polymers (long strings of some building-block molecule) that tend to be lightweight, inexpensive and resistant to degradation.

platinum     A naturally occurring silver-white metallic element that remains stable (does not corrode) in air. It is used in jewelry, electronics, chemical processing and some dental crowns.

pollutant     A substance that taints something — such as the air, water, our bodies or products. Some pollutants are chemicals, such as pesticides. Others may be radiation, including excess heat or light. Even weeds and other invasive species can be considered a type of biological pollution.

A catalyst is a chemical substance that affects the rate of a chemical reaction by altering the activation energy required for the reaction to proceed. This process is called catalysis. A catalyst is not consumed by the reaction and it may participate in multiple reactions at a time. The only difference between a catalyzed reaction and an uncatalyzed reaction is that the activation energy is different. There is no effect on the energy of the reactants or the products. The ΔH for the reactions is the same.​

Catalysts permit an alternate mechanism for the reactants to become products, with a lower activation energy and different transition state. A catalyst may allow a reaction to proceed at a lower temperature or increase the reaction rate or selectivity. Catalysts often react with reactants to form intermediates that eventually yield the same reaction products and regenerate the catalyst. Note that the catalyst may be consumed during one of the intermediate steps, but it will be created again before the reaction is completed.

Usually when someone refers to a catalyst, they mean a positive catalyst, which is a catalyst that speeds up the rate of a chemical reaction by lowering its activation energy. There are also negative catalysts or inhibitors, which slow the rate of a chemical reaction or make it less likely to occur.

A promoter is a substance that increases the activity of a catalyst. A catalytic poison is a substance that inactivates a catalyst.

• Enzymes are reaction-specific biological catalysts. They react with a substrate to form an unstable intermediate compound. For example, carbonic anhydrase catalyzes the reaction:
  H2CO3(aq) ⇆ H2O(l) + CO2(aq)
  The enzyme allows the reaction to reach equilibrium more quickly. In the case of this reaction, the enzyme makes it possible for carbon dioxide to diffuse out of blood and into the lungs so it can be exhaled.
• Potassium permanganate is a catalyst for the decomposition of hydrogen peroxide into oxygen gas and water. Adding potassium permanganate increases the temperature of the reaction and its rate.
• Several transition metals can act as catalysts. A good example of platinum in the catalytic converter of an automobile. The catalyst makes it possible to turn toxic carbon monoxide into less toxic carbon dioxide. This is an example of heterogeneous catalysis.
• A classic example of a reaction that doesn't proceed at an appreciable rate until a catalyst is added is that between hydrogen gas and oxygen gas. If you mix the two gases together, nothing much happens. However, if you add heat from a lighted match or a spark, you overcome the activation energy to get the reaction started. In this reaction, the two gases react to produce water (explosively).
  H2 + O2 ↔ H2O
• The combustion reaction is similar. For example, when you burn a candle, you overcome the activation energy by applying heat. Once the reaction starts, heat released from the reaction overcomes the activation energy needed to allow it to proceed.