Topology reconstruction from FAU to MWW structure

• Topology reconstruction from FAU to MWW structure was caused by the “synergism” of NaOH, HMI and SiO2.
• The reconstructed MCM-49 was formed gradually from exterior to interior of NaY.
• FAU/MWW co-existing structure zeolites were as the intermediate states.
• MWW zeolite was generated at the expense of FAU zeolite consumption.

Topology reconstruction from FAU to MWW structure has been explored in the presence of hexamethyleneimine, NaOH and SiO2. The samples prepared at different crystallization stages were characterized by XRD, SEM, TEM, and 29Si/27Al/13C MAS NMR to investigate the intermediates in the topology reconstruction from FAU to MWW structure. It has been demonstrated for the first time that topology reconstruction from FAU to MWW structure was caused by the “synergism” of hexamethyleneimine, NaOH, and SiO2, which was supported by transformation from FAU to SOD structure without SiO2 and the preservation of FAU structure without NaOH. It is also clearly proved that FAU structure was directly reconstructed into MWW structure by the combination of all above mentioned characterizations, especially XRD and 29Si/27Al MAS NMR. MWW structure zeolite was generated at the consumption of FAU structure zeolite, which is worthy to be noticed that solid silica gel was completely consumed at the end of topology reconstruction. As shown in SEM and TEM images, MWW structure zeolite was reconstructed gradually from exterior to interior of FAU structure zeolite, which was clearly observed by the FAU–MWW co-existing zeolites as intermediate states. The reconstructed MWW structure zeolite has high relative crystallinity.

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