Some chemical interactions themselves are very difficult or do not occur at all. And then special substances — catalysts — come to the rescue. They allow you to "get around the barrier" - and the reaction begins, although without them it would either never have started or would have occurred very slowly. There is catalysis of homogeneous and heterogeneous catalysis. What do these words mean?
The name may vary depending on whether the catalyst and reagents are in the same phase. The catalyst itself is not consumed in the reaction. If you see two phases with a boundary between the substance and the catalyst, then catalysis will be heterogeneous. The same can be said about the case when the aggregate state of a substance and a catalyst are different. Homogeneous occurs in a homogeneous medium, in one phase.
In heterogeneous catalysis, the catalyst is often a solid, and the reactants are either liquids, or dissolved in liquids, or are gases. In this case, the reagents are adsorbed on the active sites of the catalyst (do not confuse adsorption and absorption. The first means a kind of “sticking” to the surface, the second means when one substance penetrates the structure of another).
In this case, a chemical interaction occurs between the molecules of the reagent and the catalyst. It can include both a chemical reaction on the surface and a weakening of bonds within the reagent molecules. Then a reaction occurs in which the molecules of the remaining substance often strike the molecules of the first reagent. The result of the reaction is desorbed, "detaches" from the active centers. As mentioned earlier, the catalyst is not consumed in the reaction. Only the amount of reagents and products changes.
Catalysis Homogeneous and heterogeneous catalysis is widely used in industry. We give an example of the second, since theoretically we have already considered it.
As you know, margarine is saturated fat. It is solid in consistency. And vegetable fats, from which it is produced, are mostly liquid. How is hardness achieved? With the help of hydrogenation, that is, double bonds of carbon atoms become single due to the addition of hydrogen atoms. And the metal nickel in the solid state acts as a catalyst. The fats that result from this reaction are called hydrogenated. Of course, like all saturated fats, they are not very useful, but they should not be demonized either.
Catalysis homogeneous and heterogeneous catalysis must be understood, since 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 through exposure to ultraviolet radiation molecules. However, the normal process is disrupted in the presence of molecules of chlorine and fluorocarbons, which are present in the atmosphere in the form of gases and are products of industrial emissions. What happens with this? Molecules of carbon chlorine and fluorine compounds collide with ozone molecules and take one oxygen atom from them. Then, the connection of, say, chlorine with oxygen collides with another ozone molecule, resulting in an oxygen molecule and a regenerated chloro-particle, which can further destroy thousands of ozone molecules. Thus, homogeneous catalysis occurs. As you can see, knowledge of this process allows us to understand that we need to be careful with the use of certain deodorants and liquids for refrigerators.
However, it should be noted that substances that provide catalysis for homogeneous and heterogeneous catalysis can not only accelerate the reaction, but also slow it down. In this case, they are called inhibitors. And any substances, in turn, can be affected by some substances: accelerators or poisons for the catalyst. Therefore, the process of catalysis is multistage, and for its understanding it is necessary to understand the causes of catalysis. And it happens because in this process less activation energy is needed , because the process goes a different way than if it went on its own.
As we have seen, examples of catalysis can be very different in their benefits to humans. However, in order to change the world, you need to understand it. Therefore, study chemistry not only “closely”.