A Stable Silanol Triad in the Zeolite Catalyst SSZ‐70

Abstract

Nests of three silanol groups are located on the internal pore surface of calcined zeolite SSZ‐70. 2D 1H double/triple‐quantum single‐quantum correlation NMR experiments enable a rigorous identification of these silanol triad nests. They reveal a close proximity to the structure directing agent (SDA), that is, N,N′‐diisobutyl imidazolium cations, in the as‐synthesized material, in which the defects are negatively charged (silanol dyad plus one charged SiO− siloxy group) for charge balance. It is inferred that ring strain prevents the condensation of silanol groups upon calcination and removal of the SDA to avoid energetically unfavorable three‐rings. In contrast, tetrad nests, created by boron extraction from B‐SSZ‐70 at various other locations, are not stable and silanol condensation occurs. Infrared spectroscopic investigations of adsorbed pyridine indicate an enhanced acidity of the silanol triads, suggesting important implications in catalysis.

Regioselective Generation of Single‐Site Iridium Atoms and Their Evolution into Stabilized Subnanometric Iridium Clusters in MWW Zeolite

“…By carefully correlating the paired HAADF‐STEM and iDPC images, it can be concluded that Ir atoms appear in several locations, including sites at the 10MR window between the 12MR supercages and in the 12MR supercages, as illustrated in the Supporting Information, Figure S6. This is consistent with a recent work on the identification of the location of the triad silanol species in SSZ‐70, a related pure‐silica zeolite to the MWW zeolite studied in this work . In the as‐synthesized Ir@MWW‐OSDA sample, the Ir precursor is surrounded by the organic template molecules, encapsulated in the cages and cavities inside the MWW zeolite crystallites.…”

“…This is consistent with ar ecent work on the identification of the location of the triad silanol species in SSZ-70, arelated puresilica zeolite to the MWW zeolite studied in this work. [23] In the as-synthesized Ir@MWW-OSDAsample,the Ir precursor is surrounded by the organic template molecules,e ncapsulated in the cages and cavities inside the MWW zeolite crystallites.…”

Rational Manipulation of Stacking Arrangements in Three‐Dimensional Zeolites Built from Two‐Dimensional Zeolitic Nanosheets

“…A shoulder at 3728 cm −1 assigned to the intracrystalline silanols was also observed, and its intensity increased with the increasing content of disordered stacking structure. A previous study demonstrated the disordered MWW zeolite material contained two kinds of silanols on the layer surface, namely the single terminal Si‐OH and a cluster of 3 Si‐OH (Figure S13) [9a, 18] . Thus, the presence of more intracrystalline defects in MWW‐C 6 ‐SAR60 and MWW‐C 7 ‐SAR62 was consistent with the high contents of disordered stacking structure in these two materials (Figure S7).…”

Disentangling Brønsted Acid Sites and Hydrogen-Bonded Silanol Groups in High-Silica Zeolite H-ZSM-5

“…10,11 A potential overlap of1 H MAS NMR signals originating from BAS and hydrogen-bonded silanol groups has not been previously addressed. This may be in part due to the hitherto existing difficulties in separating SiOH from bridging hydroxyl groups, Si−O(H)−Al, in 1 H MAS NMR spectra.…”