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

Abstract

Tin-containing, medium pore molecular sieves (Si/Sn ratios above 40) with MEL structure have been synthesized hydrothermally and characterized by a variety of techniques. Changes in unit cell volume (XRD) account for about 20% of Sn 4 + ions in possible tetrahedral positions, l l9Sn MASNMR spectra, however, indicate that these are mostly in octahedral coordination. Framework IR spectra show an absorption at 970 cm-1 which is associated with Si-O-Sn vibration. Despite the uncertainty of the environment of the Sn 4+ ions in the silicalite structure, these tin-silicates are found to be quite active in the hydroxylation of phenol and toluene with aqueous H202 as oxidant. The product distribution suggests that most of the Sn 4+ ions are located within the channels of the MEL structure.