Germanium Atoms Exceed the Tetrahedral Coordination in MFI Zeolite.

Germanium is known to occupy tetrahedral sites by substituting silicon in germanosilicate zeolites. In this study, we present pioneering findings regarding the synthesis of zeolites with an MFI structure (GeMFI) incorporating a high germanium amount (16% Ge). Remarkably, the germanium atoms feature a slight electron deficiency with respect to GeO, and the typical coordination number of 4, as usually reported for the germanosilicate zeolites, is exceeded, giving rise to Ge dimers in a double-bridge configuration.

Variation of the Orientations of Organic Structure-Directing Agents inside the Channels of SCM-14 and SCM-15 Germanosilicates Obtained by Ab Initio Molecular Dynamic Simulations.

We report ab initio molecular dynamic simulations of the organic structure-directing agent (OSDA) in the channels of SCM-14 and SCM-15 germanosilicates for models with different germanium distribution. Since OSDA was free to move inside the channels, independent of its initial orientation after the simulations in all structures the OSDA, protonated 4-pyrrolidinopyridine, is positioned almost perpendicular to the large channels of SCM-14. The structures obtained from the dynamic simulation are more stable by 157 to 331 kJ/mol than the structures obtained by initial geometry optimization.

Visualizing the Flexibility of RHO Nanozeolite: Experiment and Modeling.

Structural flexibility is an intrinsic feature of zeolites, and the characterization of such dynamic behavior is key to maximizing their performance and realizing their potential in both existing and emerging applications. Here, the flexibility of a high-aluminum nano-sized RHO zeolite is directly visualized with in situ TEM for the first time. Variable temperature experiments directly observe the physical expansion of the discrete nanocrystals in response to changes in both guest-molecule chemistry (Ar vs CO) and temperature.