Schroeder Christian, Mück-Lichtenfeld Christian, Xu Le, Grosso-Giordano Nicolás A, Okrut Alexander, Chen Cong-Yan, Zones Stacey I, Katz Alexander, Hansen Michael Ryan, Koller Hubert
Institut für Physikalische Chemie, Westfälische Wilhelms-Universität, Corrensstrasse 28/30, 48149, Münster, Germany.
Center of Soft Nanoscience, Westfälische Wilhelms-Universität, Busso-Peus-Strasse 10, 48149, Münster, Germany.
Angew Chem Int Ed Engl. 2020 Jun 26;59(27):10939-10943. doi: 10.1002/anie.202001364. Epub 2020 Apr 23.
Nests of three silanol groups are located on the internal pore surface of calcined zeolite SSZ-70. 2D 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 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.
三个硅醇基团的簇位于煅烧后的沸石SSZ - 70的内孔表面。二维氢双/三量子单量子相关核磁共振实验能够严格鉴定这些硅醇三联体簇。实验揭示了在合成材料中，它们与结构导向剂（SDA），即N，N'-二异丁基咪唑阳离子距离很近，其中缺陷带负电荷（硅醇二元体加上一个带电荷的SiO硅氧基）以实现电荷平衡。据推断，环张力阻止了煅烧和去除SDA时硅醇基团的缩合，以避免形成能量上不利的三环结构。相比之下，通过在B - SSZ - 70的其他不同位置提取硼而形成的四联体簇不稳定，会发生硅醇缩合。吸附吡啶的红外光谱研究表明硅醇三联体的酸度增强，这表明其在催化中具有重要意义。
