CTAB modification of MCM-49 zeolite containing HMI and its acylation of anisole

A series of MCM-49 zeolite catalysts containing different amounts of the hexamethyleneimine (HMI) template were calcined at different temperatures, and then modified with cetyltrimethylammonium bromide (CTAB). Changes in structural and acidic properties were investigated by XRD, N2 adsorption, NH3-TPD, adsorbed pyridine infrared and DRIFTS measurements, and 29Si and 27Al MAS NMR. There were cleaning off of amorphous particles and extraframework Al atoms inserted into the framework of the zeolite due to the CTAB modification. These two effects resulted in more framework Al in the CTAB modified samples than the untreated samples, and a higher Brönsted acid concentration, which was confirmed by the acylation of anisole with acetic anhydride. The catalytic roles of the acid sites located in the different pore systems in the zeolite were investigated. It was verified that the active sites after CTAB modification were mainly in the HMI-free regions.

Graphical AbstractAcetic anhydride conversion over HMCM-49 after CTAB modification displayed a positive correlation with the Brönsted acid concentration, which was higher after CTAB modification than on the original HMCM-49.Figure optionsDownload as PowerPoint slide