Effect of tin precursors and crystallization temperatures on the synthesis of SBA-15 with high levels of tetrahedral tin

Abstract

Mesoporous SnSBA-15 materials with different tin precursors, crystallization temperatures, and n_Si/n_Sn ratio = 5, 10, 15, 30, 60 and 100, have been synthesized using Pluronic 123 triblock polymer [(EO)₂₀(PO)₇₀(EO)₂₀] as a structure-directing agent by simply adjusting the molar ratio of water to hydrochloric acid (n_H2O/n_HCl). The effect of the nature of the tin-ion precursor on the synthesis of SnSBA-15 has been investigated using different tin-ion precursors, viz., tin(IV) chloride pentahydrate and tin(IV) acetate. To investigate the effects on the structural and textural properties of the incorporation of tin ions, SnSBA-15 was then synthesized with different crystallization temperatures at fixed molar ratios of n_Si/n_Sn = 10 and n_H2O/n_HCl = 295 in the synthesis gel. The hydrothermal stability of SnSBA-15 was also investigated. The calcined SnSBA-15 materials were characterized by ICP-AES, XRD, N₂ adsorption, UV-vis DRS, ²⁹Si MAS-NMR, FE-SEM and TEM. The ICP-AES results show a higher amount of tin-ion incorporation on the silica pore walls, as SnSBA-15 with n_Si/n_Sn ratio up to 13.5 can be successfully prepared at a fixed n_H2O/n_HCl molar ratio of 295 by adjusting the ratio of n_Si/n_Sn in the synthesis gel. The structural and textural properties of calcined SnSBA-15 can be found from the results of XRD, and N₂ adsorption. The UV-vis DRS and ²⁹Si MAS-NMR results illustrate the effects of structure and tin-ion coordination on the SBA-15 silica pore walls while the uniform pore diameter and rope-like hexagonal mesoporous structure of SnSBA-15 can be identified from the TEM and FE-SEM images. With increasing crystallization temperature, increases of the unit cell parameter, pore size and pore volume, and decreases of the specific surface area and pore wall thickness of SnSBA-15 can be found from the results of XRD and N₂ adsorption. Finally, hexagonal SnSBA-15(5) is more hydrothermally stable than SnSBA-15(100), from the results of XRD, N₂ adsorption, and FE-SEM.