Synthesis and structural characterization of MSU-type silica–tin molecular sieves: Post-synthesis grafting of tin chlorides

Supermicroporous Sn-incorporated MSU-type silica molecular sieves, with different amounts of tin, have been synthesized using divalent and tetravalent Sn chlorides as grafting agents. The structural and chemical properties of the prepared materials, have been studied using a variety of techniques such as X-ray diffraction, N2 physisorption, FT-IR spectroscopy of chemisorbed pyridine, temperature programmed desorption of ammonia (NH3-TPD) and 119Sn Mo¨ssbauer spectroscopy. The introduction of tin produced purely Lewis acid sites on the silica surface. The amount of grafted tin was found to vary depending on the Sn precursor salt. The grafting procedure was more effective when anhydrous SnCl4 was used. A consistent part of the tin present in the MSU-Sn samples, that resulted accessible to incoming molecules, was found to reversibly change coordination number upon dehydration in He at 673 K and re-exposition to air at room temperature.