A Stable Silanol Triad in the Zeolite Catalyst SSZ-70.

Authors :: Schroeder C
Mück-Lichtenfeld C
Xu L
Grosso-Giordano NA
Okrut A
Chen CY
Zones SI
Katz A
Hansen MR
Koller H
Source :: Angewandte Chemie (International ed. in English) [Angew Chem Int Ed Engl] 2020 Jun 26; Vol. 59 (27), pp. 10939-10943. Date of Electronic Publication: 2020 Apr 23.
Publication Year :: 2020
Abstract: Nests of three silanol groups are located on the internal pore surface of calcined zeolite SSZ-70. 2D <superscript>1</superscript> H 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 <superscript>-</superscript> 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.<br /> (© 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)