A study of the acidity of SAPO-34 by solid-state NMR spectroscopy

Using multinuclear solid-state NMR in combination with probe molecule techniques, we examined the acidic property of SAPO-34 with different Si content. The results show that there are two kinds of Brønsted acid sites in SAPO-34 with the acid strength of one kind higher than that of ZSM-5. The Si species and their distribution in the framework depend on the Si content. A large amount of Si islands are formed when Si content is high, at lower Si content, only isolated Si(OAl)4 species exists. The Si content has little effects on the Brønsted acid strength of SAPO-34, but does affect the acid concentration.

Figure optionsDownload as PowerPoint slideHighlights
► There are two kinds of Brønsted acid sites in SAPO-34.
► The acid strength of one kind is higher than that of ZSM-5.
► The Si content has little effects on the Brønsted acid strength of SAPO-34.
► The Si content affects the acid concentration and the form of Si atoms in SAPO-34.