Study of the reaction of tetramethyltin with H-faujasite. Characterization of the grafted species and thermal stability

Tetramethyltin reacts very rapidly at room temperature with hydroxyl groups of H-faujasite. The reaction is relatively selective as all protons in the supercages are consumed while 85% of those in the sodalite cages and/or prisms are retained. The grafted organometallic fragment -SnMe₃ has been fully characterized by several physico-chemical methods such as volumetry, chemical analysis, infrared spectroscopy, EXAFS, solid-state NMR and ab initio calculations. X-ray diffraction and solid-state NMR studies show that the zeolite has retained its crystalline structure after reaction with the tin compound. However, its microporous volume has decreased by ca. 75%, as shown by adsorption of nitrogen and hydrocarbons, in agreement with the presence of grafted species in the microporous volume of the crystallites. Adsorption of benzene is stronger on modified zeolite than on unmodified one, due to interactions with -SnMe₃ species rather than with protons. When the reaction is carried out at higher temperature (typically 100 °C), all protons of the zeolite react, leading to a mixture of SnMe_x grafted fragments (x=1, 2, 3). Heating at higher temperatures leads to the formation of a Sn-Y zeolite which is stable under oxygen, water and hydrogen.