Structural And Surface Acidity Of The Hierarchical Composite Zeolites

Because of its adjustable solid acidity, regular channel structure, and large surface area, zeolite catalyst plays an important part in catalyzing, adsorbing, ion exchanging, etc. One of the most important characters of zeolite catalyst is its surface acidity. The types of acid, acid strength and acid distribution are all directly connected with catalytic activity of the zeolite catalyst. Therefore, studying the acid of the zeolite catalyst contributes to further understanding its catalytic mechanism of the catalytic reaction, and guides the researchers to improve and perfect the existing catalyst and prabably find more new kinds of zeolite catalyst to meet practical demands. But because of its single channel, single zeolite has certain limitations in the degree of acidity adjusting, so it cannot satisfy the requirements in the reactions. Composite zeolite catalyst has microporous, mesoporous and macroporous three-level channel structure, so it showed good synergy and catalytic fuctions. By adjusting the amount of a certain single zeolite, The acid can be changed according to requrement. For differnt kinds of composite zeolite catalyst, the differences of structure lead to different acidity. However, for same components but different ratio of composite zeolite, one part changes in amounts, the composite zeolite changes too, so does its acidity. So, studying the structure and acidity of composite zeolite has great meanings in practice.In this paper, the structures of MFC and MFZ composites of different crystalline time was characterized by XRD and FT-IR. And their acid amount, acid strength and acid types was characterized by NH3-TPD and Py-IR.The characterization results of composite MFC showed as follows: the as-synthesized MFC composites of different crystalline time has both a strong acid center and a weak acid center. It also contains a stable B acid and L acid. With the extension of crystallization time, the Y component content gradually increases, the acid strength and acid amount of the composite zeolite also increases. They are stonger than those of single zeolite catalyst.The characterization results of composite MFZ showed as follows: the as-synthesized MFZ composites of different crystalline time has both a strong acid center and a weak acid center. The Py-IR shows that the composite zeolite has B acid and L acid, and B acid is more stable. At the beginning of the crystallization, L acid is less stable. As the crystallization time extends, the amount of Y type zeolite increases, and the acid strength and amount increases too. But if the crystallization time is too long, a noise peak will occur during the synthesit process, thus affecting the acid of the composite zeolite.