In situ 11B MAS NMR study of the synthesis of a boron-containing MFI type zeolite

Abstract The transformation of porous glass spheres into MFI-spheres in a synthesis with low water content (3 moles H 2 O per mole TO 2 with T=Si, B, Al) was observed by in situ 11 B MAS NMR spectroscopy in two synthesis procedures: (i) sealed quartz ampoules containing the reaction mixture were exposed to the reaction temperature in an oven for the reaction time and then put into the spinner and analyzed at room temperature; (ii) sealed quartz ampoules containing the reaction mixture were put into the spinner, then heated up in the rotating spinner to the reaction temperature and analyzed at this temperature in dependence of the reaction time. The yield of crystalline material could be determined by means of the intensity of a narrow signal at −3.7 ppm in the 11 B MAS NMR spectra. A fast exchange exists between three- and four-coordinated boron in solution, and the relative amount of boron in both coordinations can be determined from the value of the chemical shift of the “liquid” boron signal. Thus, information about changes in the basicity of the solution could be obtained in situ from the chemical shift of the liquid boron signal. It could be shown that crystallization of the zeolite takes place with a strongly increased crystallization time under the influence of the about 10 5 -fold of the standard acceleration of gravity.