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 Q2 and Q3 states (detected by 29Si 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.