20 Examples of Positive and Negative Catalysts

It is called catalysis the chemical process by which the speed of a chemical reaction is increased by adding a substance (simple or compound) that alters reaction times without affecting the nature of the final product and without losing its own mass in the process (which is the case with reagents).

The substance that increases the speed of the reaction is called catalyst. Many chemical reactions occur very slowly, so a catalyst needs to be added to increase their speed. There are also substances that slow down chemical reactions and are called inhibitors.

Substances that increase the rate of chemical reactions are also often called positive catalysts and those that decrease it (inhibitors), negative catalysts.

Examples of positive catalyst

1. Enzymes. Naturally secreted by the body from living beings, enzymes play an important catalytic role since they accelerate vital processes that, if they occurred on their own, would require temperatures that are often incompatible with life.
2. Palladium catalysts. For cars that use unleaded gasoline, lines with palladium or platinum in small particles adhere to car exhausts, can catalyze the process of attenuation of carbon monoxide and other toxic gases of combustion, and allow them to be reduced to substances less dangerous in record time.
3. Fluorine derivatives. Accelerate the decomposition of ozone (O₃ → O + O_two) in oxygen, a reaction that is normally slow. Aerosols and refrigerants that release CFCs into the atmosphere affect the ozone layer, increasing its rate of decomposition.
4. Manganese dioxide (MnO_two). It is a frequent catalyst in the decomposition of hydrogen peroxide or hydrogen peroxide (2H_twoOR_two → 2H_twoO + O_two) in water and oxygen.
5. Nickel. It is used in the hydrogenation of vegetable oils to obtain margarine, since it accelerates the process of obtaining saturated lipids.
6. Silver. Polycrystalline silver and nanoporose are effective accelerators of carbon dioxide (CO_two) by electrocatalysis.
7. Aluminum chloride. It is used in the petrochemical industry to speed up the obtaining of synthetic resins or lubricants, without altering the delicate nature of the hydrocarbons in question, since it has acidic and basic properties at the same time (amphoteric substance).
8. The iron. It is used as a catalyst in the Haber-Bosch process to obtain ammonia from hydrogen and nitrogen.
9. UV light. Ultraviolet light, together with a specific catalyst, makes up photocatalysis: the acceleration of a chemical reaction by the work of a catalyst activated by the light energy of ultraviolet.

Examples of negative catalyst

1. Citric acid. The acid in lemon and other citrus fruits slows down the oxidation process of organic matter.
2. Enzyme inhibitors. They are 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.
3. Potassium chlorate. It is used in blueing processes, in which magnetite steel is coated to slow down or prevent its corrosion process.
4. Sorbic acid. It is a natural preservative used in the food industry to slow the decomposition of food.
5. Tetraethyl lead. In the now extinct leaded gasoline, this substance was used as an antiknock, that is, to prevent its premature explosion.
6. Propanoic acid. It is a colorless, corrosive liquid with a pungent odor, it is conducive to preserving feed, food and pharmaceutical products, as it is a powerful antifungal and inhibitor of mold growth.
7. Sulfur and derivatives. These compounds act as inhibitors of the positive catalysis of powdered platinum or nickel in hydrogenation reactions. The appearance of sulfur stops the effect and returns to its normal reaction speed.
8. Hydrocyanic (or prussic) acid. Highly toxic, its effect on animals or humans interrupts the process of numerous metalloenzymes, preventing cellular respiration and causing death in a few minutes.
9. Mercury, phosphorus, or arsenic vapor. These substances completely cancel out the action of platinum asbestos in the manufacture of sulfuric acid, acting as a powerful inhibitor.