Crystal Morphological Engineering of MFI Nanosheet Assisted by Pyrrolidone Compounds.

Abstract

Nanosheet MFI zeolite with a shortened b-axis length is highly desirable for industrial applications due to the predominant mass transfer pathway provided by its larger straight channels along the b-axis. The introduction of specific additives into the precursor fluid of the zeolite can facilitate crystal anisotropic growth. However, the range of available additives is limited, and their role and underlying mechanisms remain poorly understood. Herein, the effect of three pyrrolidone compounds on the anisotropic growth of the TS-1 zeolite is unveiled within the crystallization engineering, such as 2-pyrrolidone, N-methylpyrrolidone, and N-vinyl-2-pyrrolidinone. The effects of different water content (H₂O/SiO₂ = 40, 100, and 160), pyrrolidone compound addition (x/SiO₂ = 0.2, 0.6, 1, and 2), and seed liquid concentration on the nanosheet morphology of zeolite were studied. The TS-1 nanosheet zeolite synthesized using pyrrolidone compounds as an additive exhibits abundant high coordination titanium active sites and demonstrates excellent catalytic performance in olefin epoxidation. In this work, the crystals form a nanosheet zeolite in a nonclassical growth path. The ATS-100-1-1 sample had a thickness of 112 nm in the b-axis direction and an Lc/Lb aspect ratio of 20.08. The development of morphological engineering strategies can be extended to zeolites with other topological structures based on the intrinsic properties and interactions of additive molecules with different crystal faces.