Local Structures of Two-Dimensional Zeolites—Mordenite and ZSM-5—Probed by Multinuclear NMR

Abstract

Mesostructured pillared zeolite materials in the form of lamellar phases with a crystal structure of mordenite (MOR) and ZSM-5 (MFI) were grown using CTAB as an agent that creates mesopores, in a one-pot synthesis; then into the CTAB layers separating the 2D zeolite plates were introduced by diffusion the TEOS molecules which were further hydrolyzed, and finally the material was annealed to remove the organic phase, leaving the 2D zeolite plates separated by pillars of silicon dioxide. To monitor the successive structural changes and the state of the atoms of the zeolite framework and organic compounds at all the steps of the synthesis of pillared MOR and MFI zeolites, the nuclear magnetic resonance method (NMR) with magic angle spinning (MAS) was applied. The 27Al and 29Si MAS NMR spectra confirm the regularity of the zeolite frameworks of the as synthetized materials. Analysis of the 1H and 13C MAS NMR spectra and an experiment with variable contact time evidence a strong interaction between the charged “heads” –[N(CH3)3]+ of CTAB and the zeolite framework at the place of [AlO4]− location. According to 27Al and 29Si MAS NMR the evacuation of organic cations leads to a partial but not critical collapse of the local zeolite structure.

Nanoconfined Water in Pillared Zeolites Probed by 1H Nuclear Magnetic Resonance

“…The pore size distribution shows peaks for both samples (Figure 2b); for the MOR-P sample, the peak is centered at 4.0 nm, while for MFI-P the maximum is broader and asymmetric with the center of gravity shifted towards large sizes, possibly indicating a bimodal distribution. The results obtained are in qualitative agreement with the distances between the centers of zeolite lamellae determined from small-angle X-ray scattering (SAXS) data (4.0 and 5.2 nm, respectively) [26]. In other words, MFI-P is characterized by larger mesopores with a broader size distribution.…”

“…A detailed study of the local structure of their zeolite framework and its evolution at different preparation steps probed by multinuclear NMR was reported in Ref. [26].…”

Synthesis of Lamellar Structural Flower-like SAPO-11 Molecular Sieves with Hierarchical Pores for Enhanced Selectivity of Isomeric Alkanes in Hydroisomerization

“…Strong peaks at 39 ppm are attributed to tetrahedrally coordinated Al atoms (Al IV ), considered to be the framework species of Al. , The weak signal at −10 ppm demonstrates the existence of octahedrally coordinated Al atoms (Al VI ), which is created by adding two water molecules to the tetrahedrally coordinated Al atoms. These Al atoms are nonframework Al species. − The weak signal at 9 ppm demonstrates a small amount of pentacoordinated Al atoms (Al V ), which is formed by the coordination of a water molecule into a tetrahedrally coordinated Al species. These Al species are in transition from framework to nonframework Al species. , According to the results, most of the Al atoms were incorporated into the SAPO-11 molecular sieves’ framework.…”

Highly esthetic, deodorant, and antibacterial tile with natural zeolite set via a blast furnace slag-based geopolymer

“…Higher magnetic field shift of the peak positions for the set tile containing natural zeolite than those for the original zeolite is assumed due to change in bonding angles of siloxo and sialates frameworks (slight distortion) resulting from polymerizing together with sodium silicate and slag. 24) Nonetheless, a typical spectrum attributed to a geopolymer-derived set silicious substance is seen for the tile sample. 13) This result indicates that setting reactions among the starting materials successfully proceeded in the tiles.…”