Alkali treatment upon MCM-49 zeolite with various contents of HMI in the presence of CTAB and application in anisole acylation with acetic anhydride

Abstract

A series of MCM-49 zeolites with various contents of hexamethyleneimine (HMI), obtained by calcination at different temperatures, were alkali-treated in NaOH solution containing cetyltrimethylammonium bromide (CTAB). Changes in structural and acidic properties of the resultant samples were systematically investigated by transmission electron microscopy and scanning electron microscopy (TEM and SEM), X-ray diffraction (XRD), N2 and Ar adsorption/desorption isotherms measurements, ammonia temperature-programmed desorption (NH3-TPD) and pyridine adsorption/desorption followed by infrared measurements (Py-IR), as well as 29Si MAS NMR techniques. It was revealed that only crevices were developed on the crystals of MCM-49 zeolite samples with more HMI, resulting in the increase of acid concentrations; whereas intracrystalline mesopores (ca. 3nm) could be formed for the samples with less HMI at the expense of framework destruction. A bit of ordered mesoporous materials (OMMs) could also be detected from the latter samples, because the presence of CTAB could induce the re-assembly of dissolved species through the formation of micelle, originating from the desilication by NaOH. When the modified MCM-49 samples were used as catalysts for anisole acylation with acetic anhydride, due to the positive changes in acidities and pore structure properties, they exhibited better catalytic performances for the reaction than the unmodified HMCM-49 catalyst.