The investigation of beta polymorphs by 19F nuclear magnetic resonance

ITQ-16 (polymorphs A, B and C of beta zeolite) with different Ge content (Si/Ge=4-30) have been synthesised in fluoride medium using 4-Aza, 1-azoniabicyclo[2,2,2]octane, 1-benzyl (BzD+) as organic structure directing agent (SDA). The X-ray diffraction (XRD) patterns, present the peaks characteristic of polymorph C (zeolite ITQ-17) and (A+B) (zeolite beta) which allows to determine the percentage of the former in every sample. F− anions are incorporated into the [43 54] and double four member ring (D4R) cages of polymorphs A and B, and of polymorph C, respectively, compensating the positively charged SDA. Since the 19F nuclear magnetic resonance (NMR) chemical shift depends on the number of Ge and Si atoms and the geometry of the lodging cage, the spectra of samples ITQ-16 change, with the relative amounts of polymorphs (A+B) and C, and the Si/Ge molar ratio. The percentage of polymorph C calculated from the relative area of the 19F NMR peaks show a good, agreement with those obtained by XRD. Moreover, the detailed analysis of the spectra indicates an enrichment in Ge of the D4R units of polymorph C. The general trend observed is that the relative amount of polymorph, C increases as the Ge content in the sample increases.