What are the substances that generally make up a catalyst?

The vast majority of catalysts have three distinguishable components: the active component, the carrier, and the co-catalyst.

Active component

The active component is the main component of the catalyst, sometimes consisting of one substance, sometimes consisting of multiple substances.

Carrier

The carrier is the dispersant, binder or support for the catalytic active component, and is the skeleton for loading the active component. The catalyst made by loading the active component and the co-catalyst component onto the carrier is a loaded catalyst.

Common types of carriers: corundum, silicon carbide, pumice, diatomite, asbestos, refractory bricks for low specific surface area; alumina, SiO2-Al2O3, bauxite, white clay, magnesium oxide, silica gel, activated carbon for high specific surface area.

Co-catalyst

Co-catalysts are small amounts of substances added to catalysts, which are auxiliary components of catalysts. They have no activity or very little activity themselves, but they can change the chemical composition, chemical structure, ionic valence, acidity and alkalinity, lattice structure, surface structure, pore structure, dispersion state, mechanical strength, etc. of catalysts after being added to catalysts, so as to improve the activity, selectivity, stability and lifetime of catalysts.

The role of the carrier is similar to that of the co-catalyst in many ways, except that the amount of carrier is large and the amount of co-catalyst is small; the former is more moderate and the latter is more pronounced. In addition, due to the large amount of the carrier, the catalyst can be endowed with basic physical structure and properties such as pore structure, specific surface, macroscopic shape, mechanical strength, etc. In addition, it acts as a dispersion for both the main catalyst and the co-catalyst, especially for precious metals, which can reduce their dosage and increase their activity and reduce the catalyst cost. As a high efficiency catalyst, the selection of both active components and tailor is very important.

The activity of catalysts increases with the increase of the specific surface of the carrier In order to obtain higher activity, the active components are often loaded on a large specific surface carrier. The carrier is related to the activity, selectivity, thermal stability, mechanical strength and transfer characteristics of the catalytic process, therefore, when screening and manufacturing good catalysts.

The role of structural co-catalysts is to improve the dispersion and thermal stability of active components. The principle can make the catalytic active material smaller in size and increase the surface area to prevent or delay the reduction of activity due to sintering, etc. The industrial catalytic process usually takes place at several hundred degrees, and the unstable microcrystals are prone to sintering, thus leading to the reduction of catalyst activity. The addition of a co-catalyst can stop or slow down the growth of microcrystals, thus prolonging the life of the catalyst.

The role of electronic co-catalysts is to change the structure and chemical composition of the catalyst active material to promote catalytic activity selectivity. Principle:The empty d orbitals of the active component of the catalyst can accept electrons provided by the co-catalyst, which changes the electronic structure of the active component and improves the activity and selectivity of the catalyst; it may generate new crystalline phases, or it may also generate or increase the number of active interfaces between crystalline phases or microcrystals in the catalyst. This results in increased activity or selectivity.