Substitution of Cetyltrimethylammonium for OSDA Cations During B-SSZ-70 Zeotype Synthesis and Its Influence on Delamination

• Published in: Microporous and mesoporous materials Vol. 319; no. C; p. 111042
• Main Authors: Ramamurthy, Maya, Grosso-Giordano, Nicolás A., Hwang, Son-Jong, Xu, Le, Xie, Dan, Mishra, Manish, Okrut, Alexander, Zones, Stacey, Katz, Alexander
• Format: Journal Article
• Language: English
• Published: France Elsevier Inc 01.05.2021; Elsevier
• Subjects: Co-structure directing agent; Epoxidation catalysis; Zeolite delamination; Zeolite delamination; Co-structure directing agent; Epoxidation catalysis
• ISSN: 1387-1811; 1873-3093
• DOI: 10.1016/j.micromeso.2021.111042

We investigated the substitution of structure-directing agent diisobutylimidazolium hydroxide with cetyltrimethylammonium hydroxide (CTA+OH−) surfactant in the synthesis gel of layered-zeotype-precursor B-SSZ-70(P). At low substitution levels, CTA+ interacts with the external-zeotype surface, where it assembles. At higher surfactant amounts, CTA+ intercalation occurs, leading to swelling of the precursor material, as evidenced by powder X-ray diffraction. Characterization of adsorbed CTA+ cations by 13C MAS NMR spectroscopy demonstrates unique broad resonances in the intercalated layers, which represent a more rigid environment than in the external-surface assemblies. At still higher CTA+ substitution levels in the synthesis gel, we observe the formation of amorphous mesoporous silica. We attempted to delaminate materials synthesized with varying CTA+ substitution levels using mild conditions, in which the conventional sonication step is replaced with an easy-to-scale high-shear mixing, and in which the use of halide reagents, which are corrosive and have been required in the past, is also avoided. Our data demonstrate that synthesis of a swollen material per se is not essential as an intermediate for delamination, and that layered zeolite precursor swelling can actually undermine zeolite delamination. Our results instead point to the CTA+ external-surface assemblies as facilitating ease of SSZ-70 delamination under these mild conditions. When calcined and functionalized with grafted titanium centers, the delaminated materials are highly active and selective olefin epoxidation catalysts with organic hydroperoxides, showing a 40% higher epoxide conversion than a catalyst prepared from conventional B-SSZ-70. [Display omitted] •In the synthesis of layered zeotype precursor B-SSZ-70(P), OSDA diisobutylimidazolium hydroxide was systematically replaced with CTAOH.•At low CTAOH concentrations in the synthesis gel, CTA limits zeotype crystal growth by capping its external surface.•At high CTAOH concentrations in the zeotype synthesis gel, swelling of the resulting B-SSZ-70(P) occurs.•Delamination of the resulting materials via high-shear mixing is effective for CTA-capped materials and not effective for swollen materials.•When functionalized with titanium, the delaminated CTA-capped materials are highly active olefin epoxidation catalysts.