期刊
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION
卷 59, 期 27, 页码 10939-10943出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/anie.202001364
关键词
defects; heterogeneous catalysis; silanols; solid-state NMR spectroscopy; zeolites
资金
- Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) [KO 1817/3-1]
Nests of three silanol groups are located on the internal pore surface of calcined zeolite SSZ-70. 2D H-1 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.
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