Synthesis of tin-silicalite molecular sieves with MEL structure and their catalytic activity in oxidation reactions Original Research Article

Tin-containing, medium pore molecular sieves (Si/Sn ratios above 40) with MEL structure have been syntheszed hydrothermally and characterized by a variety of techniques. Changes in unit cell volume (XRD) account for about 20% of Sn4+ ions in possible tetrahedral positions.119Sn MAS-NMR spectra, however, indicate that these are mostly in octahedral coordination. Framework IR spectra show an absorption at 970 cm−1 which is associated with Sisingle bondOsingle bondSn vibration. Despite the uncertainty of the environment of the Sn4+ ions in the silicalite structure, these tin-silicates are found to be quite active in the hydroxylation of phenol and toluene with aqueous H2O2 as oxidant. The product distribution suggests that most of the Sn4+ ions are located within the channels of the MEL structure.