Exploring Boron Distributions in MFI-type Borosilicates

Abstract In this study, we have synthesized four MFI-type borosilicate zeolites with different B/Si ratios using tetrapropylammonium (TPA+). The preferred location of boron atoms and structural roles of TPA+ were investigated by Rietveld refinement. It revealed that boron-rich position T9 locates in the four-ring of mel composition building unit (CBU) and T5 locates in the five-rings of mfi CBU. Inspired by the structural roles of TPA+ in this series of BMFI-TPA samples, we successfully replaced TPA+ by Na+ and commercialized linear organic molecules for synthesizing MFI-type borosilicates. Using this strategy, another five BMFI samples were obtained. Two of them are well-crystallized without any impurity, which enables us to further investigate the structural information. The results show that boron-rich positions were also in the four- and five-rings. Moreover, the locations of structural-directing agents were consistent with what we expected. The preferred locations of boron atoms unravelled here may provide a new way of tailoring locations of Bronsted acids.