Application of silica gel - catalyst carrier

The main component of silica gel is silicon dioxide, whose molecular formula is usually expressed as SiO2 · nH2O, which is a material with complex pore structure. Silica gel is widely used as adsorbent, desiccant, chromatographic filler, catalyst carrier, etc. due to its porosity and wide pore size distribution, as well as a large number of silane alcohol groups covered on its surface.

In the structure of silica gel, water is connected with silicon atoms in the form of hydroxyl to form silanol group, which covers the surface of silica gel with weak acidity, selectivity and stability. It can catalyze some reactions and is mainly used for organic synthesis reactions, such as the isomerization of ethylene oxide to produce acetaldehyde. Silica gel used as catalyst has certain requirements for its particle size, shape, pore structure and stacking mode in the reactor.

Different silica gel particle sizes provide different external surfaces of catalytic activity, while pore structure determines the internal surface of catalytic activity provided by the internal pore wall. Silica gel with high porosity can provide a large number of internal surfaces.

Silica gel with large pore size is selected to make reactant molecules easy to enter and exit. For example, when melamine is produced by the atmospheric pressure gas-phase catalytic synthesis of urea, ammonia gas is used as the carrier gas, coarse porous spherical silica gel is used as the catalyst, and a fluidized bed is used.

Silica gel plays a more important role in catalyst as a carrier. Both amorphous silica gel and spherical silica gel can be used as catalyst carriers, and the extremely high purity can also prevent catalyst poisoning caused by impurities.

The catalyst is mainly composed of active substance, cocatalyst and carrier. Support is an important part of catalyst. The carrier is the dispersant, adhesive and support of the active component of the catalyst. Silica gel just has all kinds of characteristics that catalyst carrier should have. The active component shall have sufficient surface area. The dispersion of silica gel can make the active components disperse to a certain degree and keep them stable.

Secondly, it has the function of stabilizer. Silica gel has stable chemical property, good thermal stability and high specific surface area, which can increase the heat dissipation area and facilitate the heat transfer process. The support effect of silica gel can be attributed to the solid catalyst with a certain shape and size by using the carrier. It is necessary for the carrier to have a certain mechanical strength.

Silica gel has stable structure and good strength, and the active components can be distributed in the pores of silica gel. For highly active components, it can also play a dilution role to reduce the activity of the catalyst to ensure thermal balance, save the active component and reduce costs.

With the development of petroleum and petrochemical industry, silica gel as catalyst carrier has been paid more and more attention. Silica gel has such advantages as acid resistance, heat resistance, high wear resistance, etc. At the same time, due to the continuous development of new products and new processes, the carrier requirements are also getting higher and higher. The methods for loading the active components of the catalyst on silica gel include immersion method, ion exchange method, kneading method with SiO2 hydrogel, and co gel method with silicon solution.

Silica gel is widely used as catalyst carrier in petrochemical industry. Such as olefin hydration catalyst carrier, hydrogenation catalyst carrier, olefin oxidation catalyst carrier, olefin polymerization supported high efficiency catalyst carrier, olefin ammoxidation catalyst carrier.

As we all know, solid catalyst is an important catalyst widely used in organic chemical reaction and petrochemical industry. Such silica gel supports can increase the effective surface area and pore structure when used in the preparation of catalysts, which are important factors affecting the catalytic activity and selectivity. Select the appropriate carrier and preparation method to obtain effective surface area and appropriate pore structure, so that the active component has a larger exposed surface, promote particle dispersion and strengthen, thus improving the catalytic activity of the active component with small surface area.

Both fixed bed and fluidized bed catalysts require a certain mechanical strength. Some catalytic oxidation reactions are exothermic, so the catalyst carrier is required to have high thermal stability and wear resistance. Silica gel with small specific surface area or large porosity can be selected as the carrier to meet the reaction requirements. The silica gel can also be modified by introducing some metal heteroatom precursor compounds to increase its specific surface area, thereby improving the heat resistance and thermal stability of the material.

Due to the doping of metal ions in silica gel, Me-O-Si is formed, which increases the number of acid active centers and acid strength on the surface of silica gel,

so that the catalyst has specific selective catalytic activity.

The advantages of metal doped mesoporous silica gel make it have broad application prospects.