Direct synthesis of dimethyl carbonate from methanol and carbon dioxide over organotin-functionalized mesoporous benzene-silica

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.