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 synthesize d using di(cyclohexylmethyl)dimethylammonium as the template. The Ti-beta z eolite was characterized using powder XRD, UV-vis spectroscopy, FTIR, X-ray unit cell expansion, TEM, SEM, EDX, nitrogen adsorption and SAXS. The infl uence of the external surface on the catalytic activity was determined by c atalytic epoxidation experiments using surface sensitive probe molecules. Evidence was obtained for the isolated incorporation of titanium in the zeo lite lattice from X-ray unit cell expansion. The linear expansion of the un it cell volume with increasing titanium content corresponds to an average T i-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 pa rticle with an average diameter of 1.2 mu m. Sometimes a thin amorphous lay er or small particles were detected with TEM at the crystal surface. By usi ng 3,5-di-tert-butylphenyl 1-(3-methyl 2-butenyl) ether as a selective bulk y probe molecule for external surface titanium sites, it was shown that epo xidation takes place primarily at the titanium sites located at the interna l surface of the zeolite. (C) 1998 Elsevier Science B.V. FLU rights reserve d.