Catalysis homogeneous and heterogeneous catalysis: we will explain by examples

Some chemical interactions in themselvesare very difficult or do not occur at all. And then special substances - catalysts - come to the aid. They allow to "bypass the barrier" - and the reaction begins, although without them it would either never have begun or would have occurred very slowly. There is catalysis of homogeneous and heterogeneous catalysis. What do these words mean?

The name can be different,in one phase there is a catalyst and reagents. The catalyst itself is not consumed in the reaction. If you see two phases with a boundary between the substance and the catalyst, the catalysis will be heterogeneous. The same can be said about the case when the aggregate state of the substance and catalyst differ. Homogeneous occurs in a homogeneous medium, in a single phase.

In case of heterogeneous catalysis, the catalyst is often -solid, and the reagents are either liquids, or dissolved in liquids, or are gases. In this case, the reagents are adsorbed on the active centers of the catalyst (do not confuse adsorption and absorption, the first means a kind of "gluing" to the surface, the second - when one substance penetrates into the structure of the other).

In this case, between the molecules of the reagent and the catalystthere is a chemical interaction. It can include both the chemical reaction on the surface and the weakening of bonds within the molecules of the reagent. Then a reaction occurs, in which often the molecules of the remaining substance hit the molecules of the first reagent. The result of the reaction is desorbed, "peeled off" from the active centers. As already mentioned, the catalyst is not consumed in the reaction. Only the quantity of reagents and products changes.

Catalysis homogeneous and heterogeneous catalysis is widely used in industry. Let us give an example of the second, because theoretically we have already considered it.

As you know, margarine - saturated fat. It is solid in consistency. And vegetable fats, from which it is produced, are mostly liquid. How to achieve firmness? With the help of hydrogenation, that is, the double bonds of carbon atoms become single due to the addition of hydrogen atoms. And as the catalyst acts metal nickel in a solid state. Fats, which are obtained during this reaction, are called hydrogenated. Of course, like all saturated fats, they are not very useful, but demonizing them is also not worth it.

Catalysis homogeneous and heterogeneous catalysis is necessaryunderstand, because they help explain not only industrial, but also natural processes. For example, the destruction of the ozone layer is an example of homogeneous catalysis.

Ozone is destroyed and created again throughinfluence on molecules of ultraviolet irradiation. However, the normal process is disturbed in the presence of chlorine and fluorocarbon molecules, which are present in the atmosphere in the form of gases and are products of industrial emissions. What happens in this case? Molecules of chlorine and fluorocarbon compounds collide with ozone molecules and take one oxygen atom from them. Then a compound of, say, chlorine with oxygen collides with another ozone molecule, resulting in an oxygen molecule and a regenerated chlorine compound that can further destroy thousands of ozone molecules. Thus, homogeneous catalysis occurs. As you can see, the knowledge of this process allows us to understand that one must be careful with the use of certain deodorants and liquids for refrigerators.

However, it should be noted that substances,providing catalysis of homogeneous and heterogeneous catalysis, can not only accelerate the reaction, but also slow it down. In this case, they are called inhibitors. And any catalysts, in turn, can be affected by certain substances: accelerators or poisons for the catalyst. Therefore, the catalysis process is multistage, and for its understanding it is necessary to understand the causes of catalysis. And it happens because this process requires less activation energy, because the process goes on a different path than if it went by itself.

As we have seen, examples of catalysis can be very different in favor of man. However, in order to change the world, you need to understand it. Therefore, study chemistry not only "vpoglyadku."