Pure and Applied Chemistry

Abstract: Ordered periodic mesoporous benzene-silicas (Ph-PMOs) functionalized with organotin were synthesized by co-condensing (MeO)₂ClSi(CH₂)₃SnCl₃, tetraethyl orthosilicate (TEOS), and 1,4-bis(triethoxysilyl)-benzene in a Pluronic 123 acid solution. The diffraction lines for (100), (110), and (200) facets observed in their X-ray diffraction (XRD) patterns and parallel channels in their transmission electron microscopy (TEM) images show that the samples have highly ordered hexagonal array structure. The presence of bands characteristic for phenyl groups, tetrahedral and octahedral Sn species, and Qⁿ and Tⁿ species in their Fourier transform/infrared (FT/IR), diffuse reflectance UV–vis, and NMR spectra gives convincing evidence for the incorporation of phenyl groups and (MeO)₂ClSi(CH₂)₃SnCl₃ into the framework or silica wall. The organotin-functionalized Ph-PMOs exhibit much higher catalytic activity than organotin-functionalized mesoporous silica lacking phenyl groups in the framework, for direct synthesis of dimethyl carbonate (DMC) from methanol and CO₂, although both have high catalytic stability. This may be attributed to its enhanced surface hydro-phobicity and the presence of a large number of hexa-coordinated Sn species and tiny Sn oxide clusters in the former sample. The DMC yield obtained over the prepared organotin-functionalized Ph-PMOs increases monotonically with increasing CO₂ pressure. The material also exhibits high catalytic stability upon reusage.