Surface modification of active alumina catalysts-Ⅲ

2. Chemical modification method

The residual hydroxyl group and residual charge on the surface of nano active alumina catalyst can be used to select modifier purposefully for chemical reaction, change the surface structure and state, and achieve the purpose of surface modification. Common methods of surface chemical modification are as follows: coupling agent method, grafting method, grafting coating method.

(1) Coupling agent method

The surface energy of nano active alumina catalyst particles is higher than that of organic systems with lower surface energy. When they are blended, phase separation is easy to form. The solution is usually coupling technology. Coupling agents are generally compounds with bifunctional groups, which can react with inorganic and organic substances at the same time. When the coupling agent is treated, one end of the coupling agent combines with the hydroxyl group on the surface, and the other end acts with the dispersion medium.

(2) Graft method

There are active hydroxyl groups on the surface of the nano active alumina catalyst. The hydroxyl group is used as the active point of the graft reaction to graft oil soluble groups. The graft is generally small molecules. In essence, coupling treatment is also equivalent to grafting. The advantage of this method is that the amount of grafting can be controlled and the efficiency is high.

Common grafted small molecules include stearic acid, 4,4 - diphenylmethane diisocyanate, methyl - 2,4 - diisocyanate, etc.

(3) Graft coating method

Graft coating method: firstly, a layer of organic matter (mostly small molecules) is formed on the surface of nano active alumina catalyst by grafting or coupling technology, and then monomer is grafted and polymerized on the organic layer of particle surface with initiator to form an inorganic organic "core shell" structure with active alumina as the core and polymerization layer as the shell. The advantage of graft coating method is that the shell thickness can be controlled by the amount of organic compounds added.

The surface modification methods of activated alumina catalysts can be divided into physical methods and chemical methods. The modified products have better quality and wider application scope, which provides many conveniences for our industrial production and daily life.