In this blog post, we will explore the principle of how catalysts lower activation energy in chemical reactions, the structure of solid catalysts, and examples of their actual use in industry.
Activation Energy and the Role of Catalysts
The minimum kinetic energy required for molecules to meet and undergo a chemical reaction is called activation energy. Reactions with low activation energy proceed quickly because many molecules have kinetic energy greater than the activation energy of the reaction. For example, in a combustion reaction, low activation energy causes the reaction to occur easily, quickly releasing heat and light. Conversely, high activation energy slows the reaction, causing it to occur only under specific conditions.
Substances that change the reaction rate by regulating activation energy are called catalysts, and the ability to speed up the reaction rate is called catalytic activity. Catalysts provide new reaction pathways with different activation energies than those without catalysts. Catalysts increase the reaction rate by lowering the activation energy of the reaction, allowing more molecules to have sufficient energy. Catalysts do not change before or after the reaction, so even a small amount can have a large effect. Thanks to these characteristics, catalysts play an important role in various industries.
Importance and components of solid catalysts
Solid catalysts are mainly used in the chemical industry because they do not require a separate process to separate liquid or gaseous products from the catalyst. Solid catalysts are mostly composed of active ingredients, supports, and promoters. The active ingredient is a substance that provides catalytic activity by adsorbing reactants on its surface. In the catalytic action of solid catalysts, the reactants are first chemically adsorbed onto the surface of the active ingredient, and then the adsorbed reactants react on the surface and are converted into products. The reaction is completed through a process in which the products are desorbed from the surface.
Metals can be used as active ingredients in various reactions because various substances can be adsorbed on their surfaces. For example, iron is used as an active component in the synthesis of ammonia, where the reactants hydrogen and nitrogen are adsorbed onto the surface of the iron and separated into their atomic states. The adsorbed reactants are stabilized by sharing electrons with the atoms on the metal surface. The degree of adsorption of the reactants varies depending on the type of metal. The degree of adsorption must be appropriate. If adsorption is weak, the amount of adsorption is small and the catalyst activity is low. If adsorption is too strong, the adsorbed reactants become excessively stabilized, slowing down the reaction on the surface and reducing catalyst activity. In general, in solid catalysts, the more active atoms on the surface involved in the reaction, the greater the adsorption of reactants and the higher the catalyst activity.
Thermal stability of catalysts and the role of supports
Metals have low thermal stability, and at high temperatures where chemical reactions occur, small particles composed of metal atoms stick together to form larger particles, a phenomenon known as sintering. When particles sinter, the total surface area of the active metal components decreases. Supports solve this problem. By dispersing small metal particles on the surface of a support with a large surface area and high thermal stability, the decrease in catalyst activity due to sintering can be suppressed. Therefore, even a small amount of metal can increase the activity of solid catalysts that use metals as active ingredients.
Role of promoters in increasing catalyst efficiency
Promoters are added to catalysts in small amounts to regulate their activity. They can inhibit sintering by changing the surface structure of the active ingredients, or regulate the adsorption strength by changing the electron density of the active ingredients. For example, adding a small amount of ruthenium to a platinum catalyst can increase the reaction efficiency. This is because ruthenium changes the electronic structure of platinum, optimizing the adsorption and reaction rate of the reactants. Solid catalysts must contain active ingredients, but in some cases, they do not contain promoters or supports.
Actual applications of solid catalysts
Solid catalysts play an essential role in various chemical processes. For example, metals such as platinum, palladium, and rhodium are used as catalysts in automobile exhaust gas purification systems. These catalysts convert harmful exhaust gases into less harmful substances, thereby reducing environmental pollution. Catalysts are also used in the petroleum refining process to convert crude oil into useful products such as gasoline and diesel fuel. The efficiency of these catalysts is very important in terms of economic efficiency and environmental protection.
In conclusion, catalysts play an important role in increasing the reaction rate by regulating the activation energy of chemical reactions and are widely used in various fields, including the chemical industry. The appropriate combination of active ingredients, supports, and promoters in solid catalysts maximizes the efficiency of catalysts, which greatly contributes to the efficiency and environmental protection of modern industry.
