Abstract
The influence of tetrapropylammonium (TPA) ions on the structural properties of as-synthesized Ti- (TS-1) and B-containing (BOR-C) MFI zeolites crystallized from alkali-free gels is investigated. Thermogravimetric analysis shows that the negative charge of the BOR-C framework is compensated by the TPA ions, while only ‘soft’ interactions between TPA and Ti sites are observed. Rietveld analysis of the synchrotron X-ray powder diffraction patterns reveals that incorporation of Ti and B causes an expansion and a contraction of the MFI framework, respectively. Regression curves describing the unit cell parameters variation can be used to determine the real framework composition. The presence of TPA ions inside the pores strongly influences the apparent d TiO and d BO tetrahedral bond distances, which are shorter than those in the calcined forms. The mobility of the TPA cations in silicalite-1, TS-1 and BOR-C samples with the highest Ti and B content is studied by 13C NMR and molecular dynamics simulations. As expected, the TPA cation mobility increases as the pore size increases (BOR-C<S1<TS-1).
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