Role of the acidity and porosity of MWW-type zeolites in liquid-phase reaction

MWW-type zeolites, MCM-22 and ITQ-2, with a wide range of gel Si/Al ratio were synthesized and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray fluorescence (XRF), N2 adsorption and 27Al MAS NMR. Their acid properties were studied via NH3-temperature programmed desorption (NH3-TPD), 2,6-di-tert-butyl-pyridine adsorption, infrared spectra of pyridine adsorption (Py-IR), selective poisoning method as well as model acid-catalyzed reactions such as cumene cracking and 1,3,5-tri-isopropylbenzene dealkylation. It is revealed that the delamination process made the catalysts more accessible to bulky molecules but weakened their acid strength. The accessibility of acid sites plays an important role in the liquid phase reactions involving bulky molecules. ITQ-2 has high activity in isomerization of α-pinene because of its abundant accessible acid sites. While for alkylation of hydroquinone, MCM-22 is better due to its higher accessible acid sites of medium-strong strength.

The accessibility of acid sites plays an important role in the liquid phase reactions involving bulky molecules. ITQ-2 has more abundant accessible acid sites while MCM-22 possesses higher accessible acid sites of medium-strong strength.Figure optionsDownload as PowerPoint slideResearch highlights
► The acidity of MCM-22 is weakened after delamination.
► The accessibility of acid sites is greatly enhanced.
► The accessibility of acid sites is essential in liquid phase reactions.
► ITQ-2 is more efficient for weak acid catalyzed reactions.
► For medium-strong acid catalyzed ones, higher activity was obtained on MCM-22.