Direct synthesis of novel layered MCM-56 zeolite using a boron-assisted cyclohexylamine system

Abstract

Robust and environmentally friendly synthesis of two-dimensional MWW zeolites, although challenging, has been strongly desired in industry owing to their excellent performance in alkylation reactions, which benefit from short diffusion pathways. Post-synthetic treatment and/or toxic structure-directing agents such as hexamethyleneimine and piperidine are usually required for the synthesis. Here, we report a synthesis strategy for MCM-56, a delaminated MWW zeolite consisting of <3 nanosheet layers, in a one-pot approach employing low-toxicity, low-cost cyclohexylamine and H₃BO₃ as an organic template and additive, respectively. MCM-56 synthesized via this method achieves a broad range of silica-to-alumina ratios (30–80), which is significantly larger than those obtained via common approaches. Solid-state NMR experiments of ¹H, ¹¹B, and ²⁹Si with single/double resonances and heteronuclear correlation methods reveal that boron atoms are incorporated into the framework at very early stages and play a key role throughout the crystallization process to prevent the stacking of MCM-56 into MCM-49, its three-dimensional analog. A benzene/cyclohexene alkylation reaction was carried out on H-type MCM-56, which shows superior stability compared to traditional MCM-49 candidates, validating its potential for further industrial catalytic applications.