Ijobiy katalizator

Chemical reactions involving catalysts are called catalytic reactions.

Many chemical reactions may have catalytic effects. There are many catalysts and their catalytic activity is diverse. This activity is determined by the change in reaction rate due to the catalyst.

The catalyst itself is not consumed in reactions and is not a part of the end product.

There are two types of catalysis - homogenous (homogeneous) and heterogeneous (non-homogeneous) catalysis. Homogenous catalyst reacts and catalysts form a single-phase system - gas or liquid system, with no catalyst reacting surface. For example, the catalytic decomposition of hydrogen peroxide in the presence of salts (liquid phase). The rate of chemical reaction in homogenous catalysis is proportional to the catalyst concentration.

Catalyst with substances that react in heterogeneous catalysis to form a system with different phases. There is a boundary between the compound and the catalyst involved in the Bundarexia. Typically, the catalyst is solids and reactants - gases or liquids. Examples include oxidation of ammonia (gaseous phase) in the presence of platinum (solid phase) or hydrogen peroxide (liquid phase) in the presence of coal or manganese (IV) oxide (solid phase). In heterogeneous catalysis, all the reactions occur on the surface of the catalyst. Therefore, the activity of the hardener depends on the properties of its surface (size, chemical composition, formation and condition).

The mechanism of action of catalysts is usually explained by the formation of intermediate compounds by one of the reaction agents. For example, if a slow reaction is carried out in the presence of catalyst A + B = AB, then the catalyst reacts with one of the primary substances and forms an unstable intermediate:

A + K = AK

The reaction is rapid because of the low activation energy of the process. Then, the intermediate compound interacts with the primary element of the EC, which catalysts are released:

AK + B = AB + K

The surface of the catalyst is not homogeneous. It has active centers, and catalytic reactions mainly occur at these centers. Reactions occur in centers. The reacting agents are adsorbed to these centers, thus increasing their concentration on the catalyst surface. It often causes the reaction to accelerate. However, the main reason for the increase in reactivity is a dramatic increase in the chemical activity of the adsorbed molecules. Under the catalyst effect the adsorbed molecules weaken the bond between the atoms and become involved in the reaction. In this case, the reaction is accelerated by a decrease in the energy of the reaction (including the formation of intermediate compounds in the catalyst).

Some substances reduce or completely eliminate the activity of the solid catalyst. Such substances are catalytic, they are called poisons. Examples include arsenic, mercury, lead, and cyanide compounds, which are particularly susceptible to platinum catalysts. Under the conditions of production, the substances that react to the action are purified from catalytic poisons, and the toxic catalyst is regenerated (poisoned).

It should be noted that the catalyst is selectively affected, so you can get different products from one substance using different catalysts. For example, in the presence of catalyst - aluminum oxide AI₂O₃ ethylene is extracted at 300 °C with ethyl alcohol:

C₂H₅OH-> H₂0+C₂H₄