20 Examples of Positive and Negative Catalysts

Catalysis is the chemical process of acceleration or retardation of chemical reaction, from the addition of a substance or element, either simple or compound that alters reaction times without affecting the nature of the final product thereof and, in addition, without losing its own mass in the process, which does happen with the reagents.

This element is called a catalyst . Each chemical reaction has a suitable catalyst, which can accelerate, magnify or enhance ( positive catalyst ), or on the contrary slow down, diminish and weaken ( negative catalyst ) its process. The latter is often referred to as inhibitors.

Examples of a positive catalyst

1. Temperature . Most chemical reactions can be accelerated without altering their products, only by increasing the temperature of the reaction medium. For this reason the decomposition of matter occurs more rapidly in the tropics.
2. The enzymes . Segregated naturally by the body of living beings, enzymes play an important catalytic role, accelerating vital processes that, if occurring on their own, would require temperatures often incompatible with life. (see: digestive enzymes )
3. Palladium catalysts . For cars that use unleaded gasoline, conduits with palladium or platinum in small particles adhere to the exhaust of cars, can catalyze the process of attenuation of carbon monoxide and other toxic gases of combustion, allowing to reduce them to less dangerous substances in record time.
4. Derivatives of fluorine . Accelerate the decomposition of ozone (O ₃ ? O + O ₂ ) in oxygen, a reaction that is usually slow. There is the problem of aerosols and refrigerants that release CFCs into the atmosphere: they catalyze in this sense the ozone layer.
5. Magnesium dioxide (MnO ₂ ). A frequent catalyst in the decomposition of Hydrogen Peroxide or hydrogen peroxide (2H ₂ O ₂ ? 2H ₂ O + O ₂ ) in water and oxygen.
6. Nickel . Used in the hydrogenation of vegetable oils, to obtain margarine, since this metal accelerates the process of obtaining saturated lipids.
7. Silver . Polycrystalline and nanoporous silver are effective accelerators of carbon dioxide reduction processes (CO ₂ ) through electrocatalysis.
8. Aluminum Chloride . Used in the petrochemical industry to expedite the obtaining of synthetic resins or lubricants, without altering the delicate nature of hydrocarbons in question, since it has acidic and basic properties at the same time (amphoteric substance).
9. The iron . It is used as a catalyst in the Haber-Bosch process to obtain ammonia from hydrogen and nitrogen.
10. UV light . Ultraviolet light, together with a specific catalyst , composes the photocatalysis: the acceleration of a chemical reaction by a catalyst activated by the ultraviolet light energy.

Examples of negative catalyst

1. Temperature . Just as the increase in temperature accelerates chemical processes , the decrease in retards them. This is the principle of refrigeration, for example, which prolongs the life of food by keeping it at a low temperature.
2. Citric acid . Acid from lemon and other citrus fruits slows down the oxidation process of organic matter .
3. Enzyme inhibitors . Biological substances that are coupled to enzymes and reduce their activity, to stop chemical or biological processes. They are often used to fight pathogenic microorganisms , inhibiting some key process for their reproduction.
4. Potassium chlorate . Used in blueing processes, in which the magnetite steel is coated to slow or impede its corrosion process.
5. Sorbic acid . Natural preservative used in the food industry to slow down the decomposition of food.
6. Tetraethyl lead . In the already extinct leaded gasoline, this substance was used as an anti-knock, that is, to prevent its premature explosion.
7. Propanoic acid . A colorless, corrosive liquid with an acrid odor, is propitious to preserve the feed, food and pharmaceutical products, as it is a potent antifungal and inhibitor of mold growth.
8. Sulfur and derivatives . These compounds act as inhibitors of the positive catalysis of pulverized platinum or nickel in hydrogenation reactions. The appearance of sulfur stops the effect and returns to its normal reaction speed.
9. Hydric acid (or prussic) . Of very high toxicity, its effect on animals or humans interrupts the process of numerous metalloenzymes, thus preventing cellular respiration and producing death in a few minutes.
10. Vapor of mercury, phosphorus or arsenic . These substances completely cancel out the action of platinum asbestos in the manufacture of sulfuric acid, acting as a powerful inhibitor.