Heteroatom-Tolerant Delamination of Layered Zeolite Precursor Materials

Abstract

The synthesis of the first delaminated borosilicate layered zeolite precursor is described, along with its aluminosilicate analogue, which consists of Al-containing UCB-3 and B-containing UCB-4 from as-made SSZ-70. In addition, the delamination of PREFER (which is the precursor to ferrierite zeolite) under similar conditions yields delaminated layered zeolite precursors consisting of Al-containing UCB-5 and Ti-containing UCB-6. Multinuclear solid-state NMR spectroscopy (^(11)B and ^(27)Al), diffuse-reflectance UV-vis spectroscopy, and heteroatom/Si ratios measured via elemental analysis are consistent with a lack of heteroatom leaching from the framework following delamination. Such mild delamination conditions are achieved by swelling the zeolite precursor in a fluoride/chloride surfactant mixture in DMF solvent, followed by sonication. Powder X-ray diffraction, argon gas physisorption, and chemisorption of bulky base probes strongly suggest delamination, and demonstrate a 1.5-fold increase in the number density of external acid sites and surface area of calcined UCB-3, relative to calcined Al-SSZ-70. The synthesis of microporous pockets in materials UCB-3–UCB-5 suggests the possibility of interlayer porosity in SSZ-70, which is a layered zeolite precursor material whose structure remains currently unknown. The mildness of the delamination method presented here, as well as the lack of need for acidification in the synthesis procedure, enables the delamination of heteroatom-containing zeolites while preserving the framework integrity of labile heteroatoms, which could otherwise be leached under harsher conditions.