Synthesis and characterization of aluminum-free zeolite titanium beta using di(cyclohexylmethyl)dimethylammonium as a new and selective template

The aluminum-free titanium silicate analogue of zeolite beta was synthesized using di(cyclohexylmethyl)dimethylammonium as the template. The Ti-beta zeolite was characterized using powder XRD, UV-vis spectroscopy, FTIR, X-ray unit cell expansion, TEM, SEM, EDX, nitrogen adsorption and SAXS. The influence of the external surface on the catalytic activity was determined by catalytic epoxidation experiments using surface sensitive probe molecules. Evidence was obtained for the isolated incorporation of titanium in the zeolite lattice from X-ray unit cell expansion. The linear expansion of the unit cell volume with increasing titanium content corresponds to an average Ti-O bond length of 1.79 Angstrom. EDX showed a homogeneous distribution of titanium over the zeolite framework and the absence of titanium-rich phases. The morphology of the crystals as determined by SEM is a pillow-shaped particle with an average diameter of 1.2 mu m. Sometimes a thin amorphous layer or small particles were detected with TEM at the crystal surface. By using 3,5-di-tert-butylphenyl 1-(3-methyl 2-butenyl) ether as a selective bulky probe molecule for external surface titanium sites, it was shown that epoxidation takes place primarily at the titanium sites located at the internal surface of the zeolite. (C) 1998 Elsevier Science B.V. FLU rights reserved.