In this blog post, we will look at the principles and roles of catalysts that affect the speed and path of chemical reactions, as well as examples of their use in industry and the environment.
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. Substances that change the reaction rate by controlling the activation energy are called catalysts, and the ability to speed up reactions is called catalytic activity. Catalysts provide new reaction pathways with different activation energies than those without catalysts. This plays an important role in maximizing the efficiency of chemical reactions. The discovery and use of catalysts has led to important breakthroughs not only in the chemical industry but also in various scientific fields.
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. These solid catalysts can have various forms and compositions, and customized catalysts are developed according to the characteristics of the industry. For example, solid catalysts with different properties are used in petroleum refining, environmental purification, and synthetic chemistry. These catalysts increase efficiency and selectivity, which not only provides economic benefits but also has a positive impact on the environment. 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 on 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.
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, which is called sintering. When particles are sintered, the total surface area of the active metal components is reduced. 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 is suppressed. Therefore, even a small amount of metal can increase the activity of solid catalysts that use metal as an active ingredient. Alumina, silica, and zeolite are used as supports, and each support provides characteristics optimized for specific reactions.
Promoters are included in small amounts in catalysts to regulate their activity. They can inhibit sintering by changing the surface structure of the active ingredient, or regulate the adsorption strength by changing the electron density of the active ingredient. Solid catalysts must contain active ingredients, but in some cases, they do not contain promoters or supports. This is determined by the application of the catalyst and the required characteristics. For example, precious metals such as palladium, platinum, and rhodium are used as active ingredients in catalysts used to purify automobile exhaust gases, and these catalysts boast high durability and efficiency.
Catalyst research and development are constantly evolving, and new materials and nanotechnology are being used to develop more efficient and sustainable catalysts. This can greatly contribute to environmentally friendly processes and energy conservation, expanding the potential applications of catalysts beyond the chemical industry. For example, catalysts using nanoparticles exhibit higher activity than traditional catalysts due to their high surface area and unique electronic properties. These developments will play an important role in making future chemical reaction processes more efficient and environmentally friendly. The advancement of catalyst technology is expected to continue to pioneer new chemical reaction pathways and drive innovative changes in various industries.
