Chemistry is the science of substances and their transformations, as well as methods of obtaining them. Even in a regular school curriculum, such an important issue as types of reactions is considered. The classification that schoolchildren are introduced to at the basic level takes into account the change in the degree of oxidation, the phase of the course, the mechanism of the process, etc. In addition, all chemical processes are divided into non-catalytic and catalytic reactions. Examples of transformations taking place with the participation of a catalyst are encountered by a person in ordinary life: fermentation, decay. Non-catalytic transformations are much rarer for us.
What is a catalyst
This is a chemical substance that can change the rate of interaction, but does not participate in it itself. In the case when the process is accelerated with the help of a catalyst, we are talking about positive catalysis. In the event that a substance added to the process reduces the rate of the reaction, it is called an inhibitor.
Types of catalysis
Homogeneous and heterogeneous catalysis differ in phase, inwhich the starting materials are located. If the initial components taken for interactions, including the catalyst, are in the same state of aggregation, homogeneous catalysis proceeds. In the case when substances of different phases take part in the reaction, heterogeneous catalysis occurs.
Selectivity of action
Catalysis is not just a means of increasing the productivity of equipment, it has a positive effect on the quality of the resulting products. This phenomenon can be explained by the fact that due to the selective (selective) action of most catalysts, the direct reaction is accelerated, side processes are reduced. In the end, the resulting products are of high purity, there is no need to further purify the substances. The selectivity of the catalyst action gives a real reduction in non-production costs of raw materials, a good economic benefit.
Benefits of using a catalyst in production
What else characterizes catalytic reactions? Examples from a typical high school show that the use of a catalyst allows the process to be carried out at lower temperatures. Experiments confirm that it can be used to significantly reduce energy costs. This is especially important in modern conditions, when there is a lack of energy resources in the world.
Examples of catalytic production
What industry uses catalytic reactions? Examples of such productions:production of nitric and sulfuric acids, hydrogen, ammonia, polymers, oil refining. Catalysis is widely used in the production of organic acids, monohydric and polyhydric alcohols, phenol, synthetic resins, dyes, and medicines.
What is the catalyst
Many substances that are in the periodic table of chemical elements of Dmitry Ivanovich Mendeleev, as well as their compounds, can act as catalysts. Among the most common accelerators are: nickel, iron, platinum, cob alt, aluminosilicates, manganese oxides.
Features of catalysts
In addition to selective action, catalysts have excellent mechanical strength, they are able to withstand catalytic poisons, and are easily regenerated (recovered).
According to the phase state, catalytic homogeneous reactions are divided into gas-phase and liquid-phase.
Let's take a closer look at these types of reactions. In solutions, hydrogen cations H+, hydroxide base ions OH-, metal cations M+ and substances that contribute to the formation of free radicals act as an accelerator of chemical transformation.
The essence of catalysis
The mechanism of catalysis in the interaction of acids and bases is that there is an exchange between the interacting substances and the catalyst positive ions (protons). In this case, intramolecular transformations take place. According to thisreactions go like this:
- dehydration (water detachment);
- hydration (attachment of water molecules);
- esterification (ester formation from alcohols and carboxylic acids);
- polycondensation (formation of a polymer with the elimination of water).
The theory of catalysis explains not only the process itself, but also possible side transformations. In the case of heterogeneous catalysis, the accelerator of the process forms an independent phase, some centers on the surface of the reactants possess catalytic properties, or the entire surface is involved.
There is also a microheterogeneous process, which involves the presence of a catalyst in a colloidal state. This variant is a transitional state from a homogeneous to a heterogeneous type of catalysis. Most of these processes take place between gaseous substances using solid catalysts. They can be in the form of granules, tablets, grains.
Distribution of catalysis in nature
Enzymatic catalysis is fairly widespread in nature. It is with the help of biocatalysts that the synthesis of protein molecules proceeds, the metabolism in living organisms is carried out. Not a single biological process that occurs with the participation of living organisms bypasses catalytic reactions. Examples of vital processes: synthesis of proteins specific to the body from amino acids; breakdown of fats, proteins, carbohydrates.
Catalysis algorithm
Let's consider the mechanism of catalysis. This process, which takes place on porous solid chemical interaction accelerators, includesyourself a few elementary stages:
- diffusion of interacting substances to the surface of catalyst grains from the core of the flow;
- diffusion of reagents in the pores of the catalyst;
- chemisorption (activated adsorption) on the surface of a chemical reaction accelerator with the appearance of chemical surface substances - activated catalyst-reagent complexes;
- rearrangement of atoms with the appearance of surface combinations "catalyst-product";
- diffusion in the pores of the product reaction accelerator;
- diffusion of the product from the grain surface of the reaction accelerator into the core flow.
Catalytic and non-catalytic reactions are so important that scientists have continued research in this area for many years.
With homogeneous catalysis, there is no need to build special structures. Enzymatic catalysis in the heterogeneous version involves the use of various and specific equipment. For its flow, special contact apparatuses have been developed, subdivided according to the contact surface (in tubes, on walls, catalyst grids); with a filter layer; weighed layer; with moving pulverized catalyst.
Heat exchange in devices is implemented in different ways:
- through the use of remote (external) heat exchangers;
- with the help of heat exchangers built into the contact apparatus.
By analyzing formulas in chemistry, one can also find such reactions in which the catalyst is one of the end products that is formed during the chemical interactionoriginal components.
Such processes are usually called autocatalytic, the phenomenon itself is called autocatalysis in chemistry.
The rate of many interactions is associated with the presence of certain substances in the reaction mixture. Their formulas in chemistry are most often missed, replaced by the word "catalyst" or its abbreviated version. They are not included in the final stereochemical equation, since they do not change from a quantitative point of view after the completion of the interaction. In some cases, small amounts of substances are sufficient to significantly affect the speed of the process. Situations are also quite acceptable when the reaction vessel itself acts as an accelerator of chemical interaction.
The essence of the effect of a catalyst on changing the rate of a chemical process is that this substance is included in the composition of the active complex, and therefore changes the activation energy of the chemical interaction.
When this complex decomposes, the catalyst is regenerated. The bottom line is that it will not be spent, it will remain in the same amount after the end of the interaction. It is for this reason that a small amount of the active substance is quite sufficient to carry out the reaction with the substrate (reactive substance). In reality, insignificant amounts of catalysts are still consumed during chemical processes, since various side processes are possible: its poisoning, technological losses, and a change in the state of the surface of a solid catalyst. Chemistry formulas do not include a catalyst.
Conclusion
Reactions in which an active substance (catalyst) takes part surround a person, besides, they also occur in his body. Homogeneous reactions are much less common than heterogeneous interactions. In any case, intermediate complexes are first formed, which are unstable, are gradually destroyed, and regeneration (recovery) of the accelerator of the chemical process is observed. For example, when metaphosphoric acid reacts with potassium persulfate, hydroiodic acid acts as a catalyst. When it is added to the reactants, a yellow solution is formed. As you approach the end of the process, the color gradually disappears. In this case, iodine acts as an intermediate product, and the process occurs in two stages. But as soon as metaphosphoric acid is synthesized, the catalyst returns to its original state. Catalysts are indispensable in industry, they help speed up transformations and obtain high-quality reaction products. Biochemical processes in our body are also impossible without their participation.
