Gripper-like Silicon Species for Efficient Synthesis of Crystalline Metallosilicates with Spatially Homogeneous Heteroatoms in the Framework

Abstract

Heteroatoms determine the functionalities of zeolites. Facile and effective incorporation of heteroatoms into the framework of zeolites remains an important and challenging goal. We report a strategy for efficient and simple synthesis of crystalline metallosilicates with spatially homogeneous distribution of heteroatoms and free of extra-framework metal species via the crystal dissolution and crystallization process (CDC process). This method succeeds in the synthesis of a wide range of crystalline metallosilicates with the MFI topology including TS-1, Al-MFI, Fe-MFI, Sn-MFI, and Nb-MFI zeolites as well as with other topologies such as TS-2, Ti−Al−beta zeolite, and so forth. The gripper-like silicon species, which is condensed matter of silicon species in Q 2 and Q 3 states (detected by 29 Si NMR), was identified for the first time to be the key to the effective incorporation and spatially homogeneous distribution of heteroatoms during the CDC process. Such silicon species could bond heteroatoms efficiently to form stable and isolated Si−O−M structural units in the synthetic sol, and such structural units remain unchanged under the "protection" of silicon species during the whole liquid-phase transformation and crystallization process. In addition, the gripper-like silicon species could be obtained not only by dissolving the crystal under high basicity but also by dissolving/polymerizing amorphous silicon species under the same conditions. The CDC process for synthesizing crystalline metallosilicates with spatially homogeneous distribution of heteroatoms in the framework by controlling the state of silicon species opens up a new perspective for the synthesis of heteroatomic zeolites.

Rapid solvent-free synthesis of nano-sized ZSM-5 with a low Si/Al ratio at 90 °C

“…It may be associated with that the four-and five-membered silicon species in the liquid seed could fabricate a large number of crystal nuclei and bind with the monomeric Al for easier incorporation into the framework. 35,45 Note that the framework Si/Al ratio of 28 of Z3-72-28 being synthesized at 90 °C by our protocol is already much lower than the lowest value of 50 reported in the literature 22,29 for the ZSM-5 zeolites synthesized below 100 °C.…”

Synthesis–Structure–Activity Relationship in Cu-MOR for Partial Methane Oxidation: Al Siting via Inorganic Structure-Directing Agents

“…However, we do not want to exclude the very exciting possibility for these anions to influence the incorporation degree of Al into specific T-sites. Liu et al, for example, have highlighted the significance of gripper-like Si species to direct the spatial arrangement of heteroatoms, 61 a process that might very well be influenced by the presence of specific anions.…”

Functional mother liquor reversed titanium species for the green synthesis of anatase-free hollow TS-1 with tunable titanium micro-environment via a kinetic-thermodynamic co-regulatory pathway

“…However, only the weak Q 0 signal peak could be observed for the TS170-P sample. 5 Combined with Raman spectra, there are more broken and completed 4- and 5-membered rings, providing more Q 0 , Q 1 and Q 2 silica species in the mother liquor. This confirms the slower crystallization rate at low temperatures.…”

“…Many researchers have successfully synthesized TS-1, rich in TiO 4 species using various titanium and silicon resources. 4,5 In other cases, the titanium species with higher coordination have gained considerable interest due to their unique activity. Yu et al presented organic acid-and seed-assisted strategies for synthesizing TS-1 zeolites containing TiO 6 species instead of post-treatment.…”