Multiple-Quantum ¹H MAS NMR Studies of Defect Sites in As-Made All-Silica ZSM-12 Zeolite

Abstract

Multiple-quantum 1 H MAS NMR spectroscopy has been used to study defect sites in siliceous as-made ZSM-12 zeolite synthesized with perdeuterated benzyltrimethylammonium cations. The results of two-dimensional double-quantum and triple-quantum 1 H MAS NMR experiments show that three silanol (SiOH) protons of the defect site engage in hydrogen bonding with the charge-compensating siloxy (SiO -) group. Simulations of the double-quantum sideband pattern were used to determine an average dipolar coupling between the protons of 4.0 ((0.5) kHz (an equilateral triangular geometry is assumed). This value corresponds to a maximum distance of 3.1 ((0.1) Å, if the protons are rigid. We believe that these results have important implications concerning the nucleation mechanism of high-silica zeolites, as they provide new information on the structure of charge-compensating units in the zeolite colloidal precursors reported by others.

Unprecedented Zeolite-Like Framework Topology Constructed from Cages with 3-Rings in a Barium Oxonitridophosphate

“…A 31 P 2D triple-quantum (TQ) single-quantum (SQ) correlation MAS NMR spectrum 31 was obtained with a conversion period of 1.6 ms and rotor-synchronized data sampling of the indirect dimension. A 31 P{ 1 H} PostC3 3 1 -REDOR 32 curve was recorded to determine the effective dipolar coupling constant and estimate limits for the interatomic PÀH distances.…”

Assembly of Zeolites and Crystalline Molecular Sieves

“…56 These defects can be thought of as OH − + H 2 O reacting with the neutral framework to give an Si-O − (to balance the organic cation) and three SiOH groups. 57 These hydrogen-bonded clusters are observed in a variety of pure-silica structures. 56 Upon combustion of the SDA to open the pore space, the "defect" can anneal via the loss of 2H 2 O (one H + from the organic).…”

Double-Quantum Double-Quantum MAS Exchange NMR Spectroscopy: Dipolar-Coupled Spin Pairs as Probes for Slow Molecular Dynamics

“…Solving the differential equation [14] assuming that a(t) + b(t) = 1, yields the familiar exponential form of a correlation function [15] giving the relative number, b(t), of the moieties which, after a time t, are not located at their initial position. Identifying the above time, t, with a mixing time, t m , the kinetics of such a process, as expressed by Eq.…”

“…Identifying the above time, t, with a mixing time, t m , the kinetics of such a process, as expressed by Eq. [15], can be easily determined by DQ-DQ MAS exchange experiments, provided that a slow molecular motion occurs with a rate k in the order of 10…”

“…In the field of solid-state NMR, the versatility of dipolar multiple-quantum (MQ) NMR spectroscopy under magic-angle spinning (MAS) conditions has recently been demonstrated for a variety of applications (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15). The basic principle underlying the dipolar MQ MAS approach is the exploitation of dipolar couplings between spin- 1 2 nuclei for the generation of higher quantum coherences (16,17), in particular double-quantum co-herences (DQCs).…”