The rate of chemical reaction can be changed by the use of a catalyst. Most catalysts can only accelerate a chemical reaction, or a chemical reaction, and cannot be used to speed up all the chemical reactions. The catalyst is not consumed in the chemical reaction. They can be separated from the reactants either before or after the reaction. However, they are likely to be consumed at a certain stage of the reaction, and then again before the end of the reaction.

A catalyst that causes a chemical reaction to accelerate is called a positive catalyst; a catalyst that slows down the chemical reaction. For example, ester and polysaccharide hydrolysis, commonly used inorganic acid as catalyst for the oxidation of sulfur dioxide is three; five of two vanadium dioxide, commonly used as catalyst, the catalyst is a solid reactant gas, the formation of heterogeneous catalysis, therefore, the five of two vanadium is also called contact medium or contact agent; adding edible 0.01%~0.02% propyl gallic acid grease, can effectively prevent rancidity, here, propyl gallate is a negative catalyst (also called corrosion inhibitors or agent).

At present, the role of the catalyst has not been fully understood. In most cases, it is believed that the catalyst itself and the reactants participate in the chemical reaction, reducing the activation energy required for the reaction. Some catalytic reactions are due to the formation of a very easy decomposition of the "intermediate product", the decomposition of the catalyst to restore the original chemical composition, the original reactant into a. Some of the catalytic reactions are due to adsorption, which can only be carried out in the most active regions (called active centers). The greater the activity center, the stronger the activity of the catalyst. If there are impurities in the reaction, the catalyst activity may be weakened or lost.

The catalyst has a great influence on the rate of chemical reaction, and some catalysts can accelerate the chemical reaction rate to millions of times. The catalyst is selective, which can only accelerate the reaction or reaction of a certain type. For example, when heated, formic acid decomposition reaction, half of dehydration, half of the dehydrogenation:

HCOOH=H2O+CO

HCOOH=H2+CO2

If a solid Al2O3 is used as a catalyst, only the dehydration reaction occurs; if the solid ZnO is used as the catalyst, the dehydrogenation reaction is carried out separately. This phenomenon shows that different kinds of catalysts can only accelerate the chemical reaction process. Therefore, we can make use of the selectivity of the catalyst to make the chemical reaction in a certain direction.

In the catalytic reaction, the catalyst is often added to the catalyst to enhance the catalytic activity of the catalyst. Catalysts are extremely important in the chemical industry. For example, the addition of a small amount of aluminum and potassium oxide as catalyst in the synthesis of ammonia can greatly improve the catalytic activity of the catalyst.

The catalyst plays a very important role in the modern chemical industry, for example, the production of synthetic ammonia with iron catalyst, sulfuric acid production using vanadium catalyst, ethylene polymerization with butadiene rubber and three synthetic materials in production using different catalysts. According to statistics, about 90% of the chemical production process using the catalyst (such as sulfuric acid, nitric acid, ammonia synthesis, ethylene, propylene, styrene polymerization, petroleum, natural gas, coal comprehensive utilization, etc.), the purpose is to speed up the reaction rate, improve production efficiency. In the field of resource utilization, energy development, pharmaceutical manufacturing, environmental protection, catalyst also has scientists in these areas to explore the suitable catalyst in order to have a new breakthrough in some aspects. The catalyst is apparently a reaction, but as a reaction medium, the total amount of the reaction before and after the same (note, not the total amount of the reaction in the same), and so that speed up or slow down the reaction rate of a substance.

For example, there are reactions A+B=C

And A+R=X, X+B=C+R reaction, the speed will be different and the same,

R is not a change in the nature and amount of A+B=C before and after the reaction, so it can be said that R is a catalyst for the reaction.