How to form the acid center on traditional silica-aluminum molecular sieve

Aluminum-containing molecular sieves have surface acidity, and its acidity is due to the fact that Al is trivalent and Si is tetravalent, there is a pair of charges on the three-coordinated aluminum, which is the source of molecular sieves' L acid, and if in order to balance the charges, the aluminum takes on my hydroxyl group, then it becomes the source of the B acid

Silica-aluminum ratio of the molecular sieves can strongly affect its acid properties, that is to say, the amount of acid and the strength of the acid. Generally speaking, if the ratio of silicon to aluminum is increased and there is more silicon, the amount of acid will be reduced, while the strength of acid will be increased.

In addition, the molecular sieve is formed firstly as Na-type because sodium salt is used in the synthesis process, and after NH4+ ion exchange and roasting, H-type can be obtained, and H-type molecular sieve has a large amount of B-acid.

Silicon to aluminum ratio therefore has a decisive influence on the acid catalyzed reaction.