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An air purifier that applies low-temperature oxidation, where a catalyst is used to convert carbon monoxide to less toxic carbon dioxide at room temperature. It can also be used to remove formaldehyde from the air.
Process catalysis is a process that changes the rate of a chemical reaction of one or more reactants, thanks to the participation of an additive called catalysts. Unlike other reactants in a chemical reaction, a catalyst is not lost during the reaction. With a catalyst, less energy is liberated to reach the intermediate state, but the total energy released from reactants to reactants remains constant, which can speed up a chemical reaction many times over. , dozens of times, hundreds of times, should shorten the time, increase production efficiency. Biocatalysts (also known as Enzymes) are proteins that speed up chemical reactions.
A physical catalyst is a substance that changes the physical properties of the reactant. Typically lubricants or coagulants.
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Table of contents
1 Characteristics 2 In industrial production 3 Classification of catalysts 3.1 Homogeneous catalysis 3.1.1 Homogeneous catalysis theory 4 The effect of a catalyst is proportional to the concentration of the catalyst. 4.1 Acid-base catalysis 4.2 Self-catalyzed reactions 4.3 Yeast catalysis 4.4 Heterogeneous catalysis 5 Some theories about catalysts 6 References 7 Reference books
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Features < edit | edit source code>
The catalyst lowers the activation energy of the reaction.
The catalyst that catalyzes the forward reaction also catalyzes the reverse reaction, so the catalyst makes the reaction quickly reach equilibrium, does not shift the equilibrium, does not change ΔH.
In industrial production < edit | edit source code>
In nitrogenous fertilizer plants, iron is often used as a catalyst to speed up the reaction between nitrogen and hydrogen through the surface catalysis, so that nitrogen and hydrogen in the mixture easily form ammonia. If there is a catalyst, under the same conditions of temperature and pressure, the ammonia synthesis reaction will occur at a very slow rate, making it impossible to produce in large quantities.
Catalysts can help select the reaction steps that are suitable for the designed pathway, the reaction will take place in the most favorable way for the production process.
For example, when using ethyl alcohol as a raw material, depending on the choice of catalyst and reaction conditions, we can get different reaction products. If silver is selected as the catalyst and the temperature is raised to 550 °C, the ethyl alcohol will turn into acetaldehyde; if using aluminum oxide as a catalyst and at 350 °C we will get ethylene; if using a mixture of zinc oxide and chromium (III) oxide as a catalyst and at 450 °C, butylene will be obtained; If you use concentrated sulfuric acid as a catalyst and keep it at 130 – 140 °C, you will have ethyl ether.
Today, scientists have found a catalyst to make a catalytic device connected to the exhaust pipe of a car. When the car exhaust gas through the catalytic converter will be processed, the residual combustibles will be oxidized to carbon dioxide and water; nitrous oxide turns into nitrogen gas.
Catalyst classification < edit | edit source code>
Depending on the state of the components in the reaction, catalyzed reactions are divided into homogeneous catalysis and heterogeneous catalysis. Another special type of catalyst is the yeast catalyst. Yeast catalysts can be homogenous or heterogeneous. The most common homogeneous catalyst is acid-base catalysis. There are also nucleofil catalysis, electrofil catalysis, transition metal complex or its ions…
Homogeneous catalysis < edit | edit source code>
Homogeneous catalysis is a catalysis in which the catalyst is in the same phase as the reactants.
Some examples of homogeneous catalysis:
2 SO 2 + O 2 2 SO 3 +O_longrightarrow 2SO_}
2 S 2 O 3 2 − + H 2 O + 2 H ⟶ S 4 O 6 2 − + 2 H 2 O O_^+H_O+2Hlongrightarrow S_O_^+2H_O}
Homogeneous catalysis < edit | edit source code>
Shpitalsky presents five points about homogeneous catalysis:
The catalyst interacts with the reactants to form a less stable intermediate. The formation of the intermediate is a reversible reaction that proceeds rapidly. The intermediate decomposes slowly, irreversibly, forming an end product that releases the catalyst. The overall rate of a reaction is proportional to the concentration of the intermediate, not to the concentration of the reactants. The free-state catalyst concentration lies in equilibrium with the intermediate product concentration
The effect of a catalyst is proportional to the concentration of the catalyst. < edit | edit source code>
Acid-base catalysis < edit | edit source code>
The reaction in solution, especially for organic compounds, is catalyzed by many acids and bases. It is a reaction involving water, alcohol, and amines. Acidic reactions such as hydrolysis, alcoholization, ammoniaization, reactions involving carbonyl groups such as aldehydes, organic acids and their derivatives.
Self-catalysed reactions < edit | edit source code>
A reaction in which the rate is increased by the action of the reactants themselves, be they the reactants or the products, is called a self-catalysed reaction. Hydrolyzed esterification, organic acids and alcohols, self-inducible reaction. For example:
CH 3 COOC 2 H 5 + H 2 O ⟶ CH 3 COOH + C 2 H 5 OH COOC_H_+H_Olongrightarrow CH_COOH+C_H_OH}
This is an acid catalyzed reaction.
Yeast catalyst < edit | edit source code>
Yeasts (ferments, enzymes) are also catalysts (biocatalysts). Yeasts are catalysts of protein origin, that is, molecules that are made of amino acids and have a definite spatial structure of polypeptide chain. The catalytic effect is due to the fermentation processes. These are processes in which a change in the chemical composition of substances occurs as a result of the action of certain organisms, such as yeast, fungi or bacteria. In these cases the enzymes produced by the organism webgiaidap.com are the catalytically active factors. The yeast retains its activity and potency when removed from the organism webgiaidap.com.
Heterocatalysis < edit | edit source code>
A heterogeneous catalysis is a catalysis in which the catalyst is in a different phase from the reactant. Heterogeneous catalysts are usually solids and the reaction occurs on the surface of the catalyst. The most common are heterogeneous catalytic systems consisting of solid and gas phases (reactants and products).
The characteristic of heterogeneous catalysis is that the reaction takes place in many stages, with two characteristics:
The process occurs in the monomolecular layer on the surface of the catalyst. This feature is reflected in the fact that in heterogeneous catalysis, diffusion and adsorption play an important role. Catalysts are not separate molecules or ions, but rather a combination of atoms and ions.
Some theories about catalysts < edit | edit source code>
Intermediate Compound Theory: The intermediate compound theory is one of the first theories of catalysis proposed by Clement and Desormes and Sabatir. According to this theory, the reaction takes place in some form through the formation of the intermediate compound. From there, it helps us to think about catalyst selection: we have to choose which catalyst can interact with the reactant. Surface Compound Theory: The theory of surface compounds was proposed and developed by Boreskow, Temkin. According to this theory, the catalytic process can be viewed as a set of alternating stages, forming compounds and destroying them to release products. Products. However, this theory still has problems. Activity Center Theory: Based on the notion that the surface of a solid is heterogeneous. Taylor hypothesized that catalyzed reactions occur only on individual points of the surface called active sites. Taylor theory only has certain theoretical value. Polytheism: The polymorphism of heterogeneous catalysis was drafted by Balandin in 1929. This theory derives from the principle of structural correspondence between the arrangement of atoms at the surface of the catalyst and in the reactant molecule and also the corresponding energies of the bonds. According to this theory: The active site of a catalyst is a set of a definite number of adsorption centers distributed on the surface in accordance with the geometry of the converted molecules. There is formation of polyvalent complexes upon adsorption of reactive molecules on active sites. This results in a redistribution of bonds, leading to the formation of the reaction product. Activity set theory: Active set theory drafted by Kobosew in 1939. This theory is built on the idea that catalytically active substances (things) are amorphous (non-crystalline) substances consisting of a number of atoms on the surface. the non-catalytically active surface of the carrier. Up to now, the active set theory has not been accepted. Electronic theory: Pissarshewski was the first to draft the electronic theory of catalysis in 1916. This theory was forgotten until the end of 1940, but it was noticed by many people, especially in the former Soviet Union. Electron theory is based on the idea that the adsorption of reactant molecules on a catalyst depends on the distribution of energy levels within the catalyst’s crystals and on their surface.
webgiaidap.com A survey of a number of catalysis theories shows that the theory of heterogeneous catalysis has not yet reached consensus on even basic issues. The above theories are directional only for some reactions.
Reference < edit | edit source code>