Swelling and Interlayer Chemistry of Layered MWW Zeolites MCM-22 and MCM-56 with High Al Content

Swelling of layered zeolite precursors such as MCM-22P with cationic surfactants at high pH is the key step in their subsequent conversion into expanded lamellar materials by pillaring and delamination. Increasing Al content in the precursors can yield more active catalysts but affects their swelling efficiency especially at lower temperature, which was reported as favorable for layer structure preservation with more siliceous MCM-22P. The latter, a (multi)layered precursor, was investigated in this work and showed inadequate swelling of its high-Al representatives with organic hydroxide/surfactant mixtures and especially when NaOH is the source of high pH. In contrast, the unilamellar MCM-56 was found to swell readily at room temperature with various hydroxide sources, and notably with NaOH, in combination with the surfactant. The observed differences between MCM-56 and MCM-22P, especially with regard to swelling with NaOH, are attributed to the fundamentally different nature of their layer surface and interlayer linking. The former has surface terminated with ≡Al—OH–Na+ moieties, producing weak connections, instead of the pyramidal ≡Si—OHs populating the MCM-22P surface and forming interlayer H-bonding. The methods used for validating the swelling and product characterization included XRD, nitrogen sorption, IR spectroscopy and TEM imaging. The microscopy confirmed, by direct visualization, the extensive but not complete swelling of MCM-56, which can be enhanced by treatment at higher temperature.