Химия – наука о веществах и их превращениях, а also methods for their preparation. Even the usual school curriculum deals with such an important issue as the types of reactions. The classification with which schoolchildren are introduced at a basic level takes into account the change in the degree of oxidation, the phase of the flow, the mechanism of the process, etc. Moreover, all chemical processes are divided into non-catalytic and catalytic reactions. Examples of transformations that occur with the participation of the catalyst are found in man in ordinary life: fermentation, rotting. Non-catalytic transformations are much less common.
It is a chemical that can changeinteraction speed, but is not involved in it. In the case when the catalyst accelerates the process, it is a question of positive catalysis. In that case, if the substance added to the process reduces the reaction rate, it is called an inhibitor.
Homogeneous and heterogeneous catalysis differ inthe phase in which the starting materials are located. If the initial components taken for interactions, including the catalyst, are in the same aggregative state, homogeneous catalysis takes place. In the case when different phase substances are involved in the reaction, there is heterogeneous catalysis.
Катализ представляет собой не просто средство improve equipment performance, it has a positive effect on the quality of the 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. Ultimately, the products obtained are of greater purity, there is no need to further purify the substances. The selectivity of the catalyst gives a real reduction in non-production costs of raw materials, a good economic benefit.
What else is characterized by catalytic reactions?The examples considered in ordinary high school indicate that the use of a catalyst allows the process to be carried out at lower temperatures. Experiments confirm that with its help you can count on a significant reduction in energy costs. This is especially important in modern conditions, when there is a shortage of energy resources in the world.
What industry uses catalyticreaction? Examples of such industries: production of nitric and sulfuric acids, hydrogen, ammonia, polymers, oil refining. Catalysis is widely used in the preparation of organic acids, monohydric and polyhydric alcohols, phenol, synthetic resins, dyes, and drugs.
Many catalysts can act as catalysts.substances in the periodic table of chemical elements of Dmitri Ivanovich Mendeleev, as well as their compounds. Among the most common accelerators emit: nickel, iron, platinum, cobalt, aluminosilicates, manganese oxides.
In addition to selective action, catalysts have excellent mechanical strength, they are able to withstand catalytic poisons, and are easily regenerated (restored).
According to the phase state, catalytic homogeneous reactions are divided into gas-phase and liquid-phase.
Consider these types of reactions in more detail.In solutions, the chemical conversion accelerator is the H + hydrogen cations, OH– base hydroxide ions, M + metal cations, and substances that promote the formation of free radicals.
Mechanism of catalysis in the interaction of acids andThe reason is that there is an exchange between the interacting substances and the catalyst with positive ions (protons). When this occurs, intramolecular transformations. For this type of reaction are:
Catalysis theory explains not only the process itself,but also possible side transformations. In the case of heterogeneous catalysis, the process accelerator forms an independent phase, some centers on the surface of the reactants have catalytic properties, or the entire surface is involved.
Существует и микрогетерогенный процесс, который involves the presence of a catalyst in the colloidal state. This option is a transitional state from homogeneous to 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.
Enzymatic catalysis is quite widecommon in nature. It is with the help of biocatalysts that the synthesis of protein molecules takes place, the metabolism in living organisms is carried out. Not a single biological process involving living organisms bypasses the catalytic reactions. Examples of vital processes: synthesis of amino acids from proteins specific to the body; splitting of fats, proteins, carbohydrates.
Consider the mechanism of catalysis. This process, which takes place on porous solid accelerators of chemical interaction, includes several elementary stages:
Catalytic and non-catalytic reactions are so important that scientists for many years continue to research in this area.
При гомогенном катализе нет необходимости construct special structures. Enzymatic catalysis for a heterogeneous variant involves the use of diverse and specific equipment. For its flow, special contact devices have been developed, subdivided along the contact surface (in tubes, on walls, catalyst grids); with a filtering layer; suspended layer; with moving pulverized catalyst.
Heat transfer in the apparatus is implemented in different ways:
Analyzing formulas in chemistry, one can find such reactions in which one of the final products, which is formed during the chemical interaction of the initial components, acts as a catalyst.
Such processes are called autocatalytic, the phenomenon itself in chemistry is called autocatalysis.
Скорость многих взаимодействий связана с the presence in the reaction mixture of certain substances. Their formulas in chemistry are most often overlooked, replaced by the word "catalyst" or its abbreviated version. They are not included in the final stereochemical equation, since they do not change from the 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. Such situations are also quite possible when the reaction vessel itself acts as an accelerator of chemical interaction.
The essence of the influence of a catalyst on the change in the rate of a chemical process is that this substance is included in the active complex, and therefore changes the activation energy of a chemical interaction.
With the collapse of this complex is observedcatalyst regeneration. The bottom line is that it will not be spent, it will remain in the same quantity after the end of the interaction. It is for this reason that an insignificant amount of the active substance is sufficient to carry out the reaction with the substrate (reactive substance). In reality, insignificant amounts of catalysts are still consumed in carrying out chemical processes, since various side processes are possible: its poisoning, technological losses, and the change of the surface state of a solid catalyst. Chemistry formulas do not imply the inclusion of a catalyst.
Reactions in which the active participatessubstance (catalyst), surround the person, besides they flow in his body. Homogeneous reactions are much less common than heterogeneous interactions. In any case, the formation of intermediate complexes occurs first, which are unstable, are gradually destroyed and regeneration (restoration) of the accelerator of the chemical process is observed. For example, in the interaction of metaphosphoric acid with potassium persulfate, hydroiodic acid acts as a catalyst. When it is added to the reactants, a yellow solution is formed. As we 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 accelerate transformations, to obtain high-quality reaction products. The biochemical processes in our body are impossible without their participation.
